Black tank vent pipe too long reducing capacity. DIY fix advice requested

[Kemper]

Hello,

I've had my GD Imagine 22MLE for over a year and have always been suspicious of how often I have to empty the black tank. I'm mostly by myself and have to empty the tank every 3 days.

I bought a water flow meter to put a known amount of water in my 37 gallon black tank. I emptied and cleaned it out as best I could and put 15 gallons down the toilet in using a garden hose with the flow meter.

I turned on the trailer's fresh water supply, filled the bowl and flushed. Immediately the toilet burped at me indicating it was full. I used a dowel as a dip stick to see how deep the water was in the tank: 3.5 inches.

Most 37 gallon black tanks on the market are 7" or deeper. Not sure about the model in my trailer, but based on the water depth at 15 gallons I put it, it seems to be near 7".

Next I went on the roof and pulled the vent cover. I snaked a measuring tape down the vent pipe until I hit bottom of the black tank. Then I carefully lifted the measuring tape to catch it on the bottom lip of the vent pipe. It was 1.5 inches from the bottom. I repeated the measurement a couple of times to verify.

It seems clear to me that I need to shorten the vent pipe to keep it from protruding so far into the black tank. But how? I want to do it myself in the easiest, least destructive way possible.

I've identified the interior wall containing the vent pipe. I think I can open the wall but it's going to be a pain (pulling trim pieces and many wall staples). I don't want to have to drop the black tank. I'd consider pulling the vent pipe up through the vent cover and chopping off the excess but I'm not sure how it's attached at the tank (friction fit gasket?) or supported in the wall.

Any advice would be greatly appreciated

Kemper
Tow vehicle: 2022 Toyota Tundra
Coach: 2023 Imagine XLS 22MLE
Central Florida

 

[Tom Traveler]

It seems clear to me that I need to shorten the vent pipe to keep it from protruding so far into the black tank. But how? I want to do it myself in the easiest, least destructive way possible.

That was an astute way of measuring the vent pipe extension into the black tank. I can see how the long vent pipe could cause issues - burping when flushing the toilet, excess odor, and restricted flow when emptying.

Regarding a fix - it seems to me you will need to be able to access the point where the vent pipe enters the black tank. On our Solitude, it goes in through a sliding seal. It is not glued. if you can get a bit of room there, maybe you could cut the pipe several inches above where it enters the tank. Pull the cut piece out of the tank to determine the correct length. Cut off the excess, insert the now shorter piece back into the tank, and glue it back onto the vent pipe with an ABS coupler. You could also use a flexible clamp type coupler. If this works, you wouldn’t need to uncover the entire length of the pipe in the wall.

You do have one advantage over me. It sounds like your toilet sits directly over the black tank. On the 380FL, it is offset so you can’t use a dipstick or a hose wand.

 

[Riverbug]

Hi [MENTION=54094]Kemper[/MENTION]. This may be of some use to you...

The location of our vent pipe is a main wall that I preferred not to tear into and have to cover up. But also found that the way they installed the pipe restricted me from being able to pull the pipe up through the seal. Take a look at my post and see if it of any use. You can scroll down to find my resolution with some pictures.

https://www.mygrandrv.com/forum/showthread.php/51157-Possible-Vent-Pipe-Slippage

 

[Tom Traveler]

Hi [MENTION=54094]Kemper[/MENTION]. This may be of some use to you...

The location of our vent pipe is a main wall that I preferred not to tear into and have to cover up. But also found that the way they installed the pipe restricted me from being able to pull the pipe up through the seal. Take a look at my post and see if it of any use. You can scroll down to find my resolution with some pictures.

Riverbug, I read the other post. You get the DIY of the Month award. I had a couple of questions I asked there and I'll repeat here as the older post may escape your notice.

How would you have been able to drop the tank with that adapter glued to the vent pipe inside of the tank? Wouldn't the tank hang up on the vent pipe?

By the way, are you happy with your SeeLevel sensors and how much trouble was the instllation. The OEM sensors are next to worthless. I never really know what the level in the black tank is.

 

[huntindog]

Hello,

I've had my GD Imagine 22MLE for over a year and have always been suspicious of how often I have to empty the black tank. I'm mostly by myself and have to empty the tank every 3 days.

I bought a water flow meter to put a known amount of water in my 37 gallon black tank. I emptied and cleaned it out as best I could and put 15 gallons down the toilet in using a garden hose with the flow meter.

I turned on the trailer's fresh water supply, filled the bowl and flushed. Immediately the toilet burped at me indicating it was full. I used a dowel as a dip stick to see how deep the water was in the tank: 3.5 inches.

Most 37 gallon black tanks on the market are 7" or deeper. Not sure about the model in my trailer, but based on the water depth at 15 gallons I put it, it seems to be near 7".

Next I went on the roof and pulled the vent cover. I snaked a measuring tape down the vent pipe until I hit bottom of the black tank. Then I carefully lifted the measuring tape to catch it on the bottom lip of the vent pipe. It was 1.5 inches from the bottom. I repeated the measurement a couple of times to verify.

It seems clear to me that I need to shorten the vent pipe to keep it from protruding so far into the black tank. But how? I want to do it myself in the easiest, least destructive way possible.

I've identified the interior wall containing the vent pipe. I think I can open the wall but it's going to be a pain (pulling trim pieces and many wall staples). I don't want to have to drop the black tank. I'd consider pulling the vent pipe up through the vent cover and chopping off the excess but I'm not sure how it's attached at the tank (friction fit gasket?) or supported in the wall.

Any advice would be greatly appreciated

Kemper
Tow vehicle: 2022 Toyota Tundra
Coach: 2023 Imagine XLS 22MLE
Central Florida

I have been into the plumbing on my momentum. It's 52 gallon tanks are 7" on the deep end, tapering to 3.5" on the shallow end. As far as the vent pipe goes, they use a rubbber grommet that the pipe is inserted into.(friction fit) It has a lip that prevents it from protruding into the tank very far. Probably an inch or so. I am not sure that a tape measure snaked in from the roof can tell you much. that pipe may not be a straight shot into the tank. I know that mine has some bends in it.

 

[Riverbug]

Riverbug, I read the other post. You get the DIY of the Month award. I had a couple of questions I asked there and I'll repeat here as the older post may escape your notice.

How would you have been able to drop the tank with that adapter glued to the vent pipe inside of the tank? Wouldn't the tank hang up on the vent pipe?

By the way, are you happy with your SeeLevel sensors and how much trouble was the instllation. The OEM sensors are next to worthless. I never really know what the level in the black tank is.

Hey Tom. I’ll answer here tonight and maybe also respond in the other thread too in case someone comes across that one later and finds it helpful.

Since I was able to turn and lift the vent pipe at the roof at least until the seal met the underside of the floor at the top of the tank, I’m guessing that if I had chosen to drop the tank, the vent pipe would have slipped down with it. Then a person could cut the pipe near the tank, pull the seal, and remove the adapter from inside the tank. At that point it would probably be easiest to get a new pipe that would stick out the roof and be cut off at the right length once the tank, seal, and pipe were back in place. I had just finished putting the entire underbelly back in place, and sealing everything up. I just didn’t want to take it all back apart, cut the drain pipes and drop the tank so I chose the route I went. And we were getting ready to depart on a two month trip.

We love the SeeLevel sensors. After boondocking many weeks since installing them, we find them extremely helpful. It’s nice to know the actual percentage of each tank. Installation isn’t too bad, but I already had the belly open for the solar, inverter, tank heat pads, and some other mods that I did. So the sensors were one of the easier projects I did at that time. You basically need a power source and ground to the monitor panel, then run a positive wire from each sensor to the panel and attach the ground wire from each sensor to the frame. As usual, running the wires is the most time consuming.

 

[Riverbug]

I have been into the plumbing on my momentum. It's 52 gallon tanks are 7" on the deep end, tapering to 3.5" on the shallow end. As far as the vent pipe goes, they use a rubbber grommet that the pipe is inserted into.(friction fit) It has a lip that prevents it from protruding into the tank very far. Probably an inch or so. I am not sure that a tape measure snaked in from the roof can tell you much. that pipe may not be a straight shot into the tank. I know that mine has some bends in it.

Hi [MENTION=12888]huntindog[/MENTION] If you take a look at my other thread you’ll see that what you describe as the way they should assemble the vent pipes is not always the case, unfortunately. Sometimes the adapter that should sit on top of the seal to prevent it from sliding down is actually put inside the tank preventing the pipe from being pulled up as well as venting correctly.

 

[traveldawg]

This (and the associated post) makes for an interesting and educational read. I just have one question....

How did GD manage to put the seal inside the tank instead of on the outside?

I figure if the seal wouldn't pull back up through the tank someone at GS must have been a contorstionist to get the seal on the pipe on the inside of the tank.

 

[Tom Traveler]

This (and the associated post) makes for an interesting and educational read. I just have one question....

How did GD manage to put the seal inside the tank instead of on the outside?

I figure if the seal wouldn't pull back up through the tank someone at GS must have been a contorstionist to get the seal on the pipe on the inside of the tank.

RiverBug, please correct me if I have this wrong. I don't think GD put the seal inside the tank. From Riverbug's pictures it looks like they glued the lip to the pipe below the seal instead of above it.

The sliding seal makes sense assuming there is nothing glued to the pipes (no lips or other protrusions) below the seal. That allows one to drop the tank - it simply slides off of the pipes. In Riverbug's case, I don't think he would have be able to drop the tank without problems because it would have hung up on the lip glued to the vent pipe below the seal. That had to be a real bonehead move on the part of an installer but I'm not surprised. As they build these things from the bottom up, nothing in the future assembly would have caught the problem.

 

[Riverbug]

This (and the associated post) makes for an interesting and educational read. I just have one question....

How did GD manage to put the seal inside the tank instead of on the outside?

I figure if the seal wouldn't pull back up through the tank someone at GS must have been a contorstionist to get the seal on the pipe on the inside of the tank.

I really don't know. I can only think that the seal is placed over the pipe before they glued the end piece on then fit the seal onto the tank with the end piece already inside the tank. Not sure how else it could have been done, but however it was done it was a boneheaded thing to do.

 

[Riverbug]

RiverBug, please correct me if I have this wrong. I don't think GD put the seal inside the tank. From Riverbug's pictures it looks like they glued the lip to the pipe below the seal instead of above it.

The sliding seal makes sense assuming there is nothing glued to the pipes (no lips or other protrusions) below the seal. That allows one to drop the tank - it simply slides off of the pipes. In Riverbug's case, I don't think he would have be able to drop the tank without problems because it would have hung up on the lip glued to the vent pipe below the seal. That had to be a real bonehead move on the part of an installer but I'm not surprised. As they build these things from the bottom up, nothing in the future assembly would have caught the problem.

You are correct. The seal is affixed to the tank as it should be - there is a grove in the seal where it fits onto the hole in the tank. The seal was not inside the tank, it was sealed just fine. The only problem was the adapter being glued inside under the seal.

 

[IBEW Sparky]

You are correct. The seal is affixed to the tank as it should be - there is a grove in the seal where it fits onto the hole in the tank. The seal was not inside the tank, it was sealed just fine. The only problem was the adapter being glued inside under the seal.

After reading and rereading both of these threads this is my take on it. The adapter is designed for the smaller end (bottom) to go through the grommet and the wider section should fit tightly in to the section of grommet outside of the tank. This "adapter" isn't much different than what is call the "bell end" of an electrical PVC conduit, as it is molded that way with a slightly rounded edge where it increases in size with the top edge being a flat cut without any rounded edges. It was definitely glued onto the pipe prior to it being installed into the grommet. At some point during assembly the pipe was set into the grommet and was simply pushed too far letting the slightly curved molded edge be forced through the grommet. Had it been noticed at the time of installation the grommet would probably have been flexible enough to pop the adapter back out of grommet. Trying to pull the adapter out after the fact and you have the top edge of the adapter getting stuck on the bottom edge of the grommet. Had you put the metal rod directly through the center of the pipe sticking above the roof you may have been able to use it to pull up and twist the pipe and pop it out of the grommet useing more force. The downside is you chance pulling the entire grommet out of the the tank with the pipe. My only concern with your remedy of drilling the holes into the fitting is that the burrs and edges will eventually get enough TP and stuff stuck to them that you'll start seeing a reduction in tank capacity before it starts "burping" again.

Pipe adapter with slightly rounded edge.



Factory grommet...



On my 337RLS it wouldn't have been possible to pull the pipe up through the roof as it doesn't go straight up and out. After measuring it several times using the exact center of the bathroom exhaust fan as a reference point I've determined it goes up into the ceiling, cavity has a 90° elbow on it and then runs about 18" towards the rear of the RV where it turns up 90° and goes through the roof. It actually protrudes through the roof about even with the front edge of the upper buffet cabinets. Why they installed it like that is beyond me... possibly to prevent the pipe from every being able to drop down into the tank any further.

 

[RetiredWeR]

I have a 2015 323BHS. I had a leak behind the wall in the bathroom. I removed the wall and found the vent pipes from all 3 tanks come together. The left went to the Black tank the middle went to the Kitchen gray and the right went to the Shower black.

 

[Riverbug]

Had you put the metal rod directly through the center of the pipe sticking above the roof you may have been able to use it to pull up and twist the pipe and pop it out of the grommet useing more force. The downside is you chance pulling the entire grommet out of the the tank with the pipe. My only concern with your remedy of drilling the holes into the fitting is that the burrs and edges will eventually get enough TP and stuff stuck to them that you'll start seeing a reduction in tank capacity before it starts "burping" again.

With all the force I could muster, I was not able to pull the pipe up through the seal. That's when I determined it was either drop the tank (and all that entails) or go the route I chose to. Been working fantastic so far. If I have problems in the future I'll have to take my lumps and drop the tank, but I don't really expect it to be an issue.

 

[Kemper]

Problem solved!

Kemper here with an update on this project:

I opened the internal wall where the vent pipe passes from the roof down into the black tank. Then I used a Dremel tool to cut the vent pipe down below the gasket in the black tank. Using a rope passed through the pipe/coupler, I pulled the cut-off section up through the toilet.

I then reused the pipe/coupler by pushing it down into the grommet and used a couple of Fernco pipe couplers to rejoin the vent pipe. (I also had to cut the vent pipe sections to get everything to fit properly.)

Now I need to close the wall back up and this project will be complete. I've omitted some details (and several dead ends) but I'd be happy to answer any questions.

Thank you all for your tips and suggestions. I couldn't have done it without your help.

 

[huntindog]

After reading and rereading both of these threads this is my take on it. The adapter is designed for the smaller end (bottom) to go through the grommet and the wider section should fit tightly in to the section of grommet outside of the tank. This "adapter" isn't much different than what is call the "bell end" of an electrical PVC conduit, as it is molded that way with a slightly rounded edge where it increases in size with the top edge being a flat cut without any rounded edges. It was definitely glued onto the pipe prior to it being installed into the grommet. At some point during assembly the pipe was set into the grommet and was simply pushed too far letting the slightly curved molded edge be forced through the grommet. Had it been noticed at the time of installation the grommet would probably have been flexible enough to pop the adapter back out of grommet. Trying to pull the adapter out after the fact and you have the top edge of the adapter getting stuck on the bottom edge of the grommet. Had you put the metal rod directly through the center of the pipe sticking above the roof you may have been able to use it to pull up and twist the pipe and pop it out of the grommet useing more force. The downside is you chance pulling the entire grommet out of the the tank with the pipe. My only concern with your remedy of drilling the holes into the fitting is that the burrs and edges will eventually get enough TP and stuff stuck to them that you'll start seeing a reduction in tank capacity before it starts "burping" again.

Pipe adapter with slightly rounded edge.

View attachment 49186

Factory grommet...

View attachment 49187

On my 337RLS it wouldn't have been possible to pull the pipe up through the roof as it doesn't go straight up and out. After measuring it several times using the exact center of the bathroom exhaust fan as a reference point I've determined it goes up into the ceiling, cavity has a 90° elbow on it and then runs about 18" towards the rear of the RV where it turns up 90° and goes through the roof. It actually protrudes through the roof about even with the front edge of the upper buffet cabinets. Why they installed it like that is beyond me... possibly to prevent the pipe from every being able to drop down into the tank any further.

I used that grommet when I added a tank. Having never seen one before, I got an extra and set up a test rig. I had some aluminum sheet the same thickness as the tank. I measured the grommet to determine what size hole was needed. drilled the aluminum sheet. Installed the grommet in it. Then I soaped up a short piece of the the pipe and pushed in into the grommet. It could only go in until it hit the back lip of the grommet. It is a very tight fit. That pipe cannot fall into the tank. And I could not pull it out of the grommet either. That pipe is not gonna budge,,,,and no adaptor is needed. I think the issue you all are having is caused by people using an adaptor that isn't supposed to be there.

On edit: I just looked on GD parts lookup. There is not an adaptor listed for my unit.

 

[Riverbug]

I used that grommet when I added a tank. Having never seen one before, I got an extra and set up a test rig. I had some aluminum sheet the same thickness as the tank. I measured the grommet to determine what size hole was needed. drilled the aluminum sheet. Installed the grommet in it. Then I soaped up a short piece of the the pipe and pushed in into the grommet. It could only go in until it hit the back lip of the grommet. It is a very tight fit. That pipe cannot fall into the tank. And I could not pull it out of the grommet either. That pipe is not gonna budge,,,,and no adaptor is needed. I think the issue you all are having is caused by people using an adaptor that isn't supposed to be there.

On edit: I just looked on GD parts lookup. There is not an adaptor listed for my unit.

I don't know if I agree necessarily that it has as much to do with the factory using the adapter (perhaps that is true), but the adapter certainly should not find its way inside the tank under the grommet whether installed that way or slipping down. In my case, it had to be installed that way because the pipe on the roof was still just under the cap. Had the pipe slipped down, then it would have had to be too long to fit under the cap on the roof and still be 2 inches from the bottom of the tank.