Gray tanks allow drain, black tank fine

[hampal]

Both of my gray tanks are draining incredibly slow but the black tank drains like gangbusters.

My sewer hose is going over a low curb before it gets to the sewer so I have to lift the hose and walk the last bits of water out of it to make it drain into the sewer. I've noticed that the water wants to run a little bit back uphill as I'm doing that. It makes me think that there's some suction or vacuum on the other end. Could a blockage on the roof vent cause this? I think if the roof vent were blocked it would slow down the black tank drainage too but that's coming out at full force.

 

[Gronk1]

What trailer model do you have? My 310GK's kitchen grey tank drains slow. The dump line has very little slant to it.
Black tank pipes are bigger than grey ones also.
I've read on here that if you lower the front of the trailer will help with flow. Not that important to me so I've never tried it.

 

[Keebler]

May be worth trying this: https://www.amazon.com/Camco-Blaster-Rinser-Backflow-Preventer/dp/B00T36KRS2/ref=sr_1_1?crid=3RRBJBK98X4OM&dib=eyJ2IjoiMSJ9.2Fcc7wkfqbaVrf5vxzw8O_BCNrBZTnex6MXIylthze9Oet4nBtYBz8WH4vJrm0K_YBPc2fwTKc3dnEr87JVBKrZqCVUbnSvHThXjQb5rRJKvXPmpdhiP5h76xYu-l9fa5rApc1J7_ayebzCMxkP97AfBS7rYCpT5A5YrS947-KztIENMAuE3SHwnI-dbIVArTwdgmPUwjuZeMcW5GU29kZuIZNatDFh7nHUbcSvO3TuupC3cBRK_mzUeDRWmbRp5aJwtTtw21LUGsyq_4__HwHSbiUi5pnjV9Hf8mpsX0aI.jKdKVEE_Hy6U1803qHLfKvKB6ICce-HmiC4Xh53KV_k&dib_tag=se&keywords=rv%2Bclear%2Bsewer%2Bwith%2Brinse&qid=1718992388&sprefix=rv%2Bclear%2Bsewer%2Bwith%2Brinse%2Caps%2C112&sr=8-1&th=1

I'd do it with all the gates closed; then 1 open at a time.

Regardless of fixing this; once you use this on your black tank after you think you've cleaned it; you will use this every time.

 

[hampal]

What trailer model do you have? My 310GK's kitchen grey tank drains slow. The dump line has very little slant to it.
Black tank pipes are bigger than grey ones also.
I've read on here that if you lower the front of the trailer will help with flow. Not that important to me so I've never tried it.

It's a 2020 Imagine 2500 RL. Normally when I open the grey tank valves the outrush of water completely fills the line but this trip it's little more than a trickle and takes 20 minutes to completely empty each grey tank.

 

[Gronk1]

It's a 2020 Imagine 2500 RL. Normally when I open the grey tank valves the outrush of water completely fills the line but this trip it's little more than a trickle and takes 20 minutes to completely empty each grey tank.

Ruh roh.
I'd try what [MENTION=8240]Keebler[/MENTION] suggested. I use one of those also.

 

[kb0zke]

We've used one similar for nearly 10 years. It started leaking a bit, so I bought one of those at Wal-Mart. Works fine. Our trailer has a black tank rinse system, but there is a bit of a leak at the point where the hose attaches, so I haven't used it for a while. We're parked for a month, so will have time to tear into it a see what's what.

On our trailer, the two grey tanks come from opposite ends and the black is in the middle, so the spray at the drain point goes straight into the black tank, while it has to angle to go into the grey tanks. I don't worry about getting them all that clean, as I dump when I need to fill. (We run only on the fresh water tank.)

 

[hampal]

What about the symptom where trying to remove standing water from the sewer hose by walking it towards the sewer? It seems like it wants to get sucked back uphill towards the trailer.

I'm home now and went up on the roof and took a picture. If allowed I'll post it here. There are three things on the roof that look like they could be tank vents. One is white and two are black. One black one is directly above the back of the toilet and has no cap on it. Is it supposed to have a cap? The other two are capped. Nothing visibly appears to be blocked.



#1 is above the front of the shower
#2 I have no idea what is below it but its somewhere in the bathroom
#3 is directly above the back of the toilet and I assume its the black tank vernt.

#3 has no cap. Should it have one?

Which one would be the vent for the grey tanks?

 

[hampal]

More bizareness. The tank that was reading 2/3 full, I completely emptied when I got home. It trickle drained for about half an hour and I got maybe 3/4 of a gallon to 1 gallon in my tote. When I went back to the panel to see what it was reading, it was now reading empty.

 

[Dutchman2]

More bizareness. The tank that was reading 2/3 full, I completely emptied when I got home. It trickle drained for about half an hour and I got maybe 3/4 of a gallon to 1 gallon in my tote. When I went back to the panel to see what it was reading, it was now reading empty.

Good chance the grey tank was actually close to empty but there was a piece of debris stuck to a sensor creating the false level reading. Very common issue with tank sensors.

Dutchman2

 

[livinthelife]

More bizareness. The tank that was reading 2/3 full, I completely emptied when I got home. It trickle drained for about half an hour and I got maybe 3/4 of a gallon to 1 gallon in my tote. When I went back to the panel to see what it was reading, it was now reading empty.

tank sensors are notoriously incapable of telling how full/empty you are.

 

[kb0zke]

We always just use our fresh water tank, so when the fresh water is getting low that means the other tanks are getting full. The fresh water sensors generally will be pretty good, so that's good enough for us.

 

[IBEW Sparky]

We always just use our fresh water tank, so when the fresh water is getting low that means the other tanks are getting full. The fresh water sensors generally will be pretty good, so that's good enough for us.

Not necessarily... it depends on the size of your tanks. On my 5er I have a 60 gallon fresh water tank, but I also have (2) 45 gallon grey tanks and a 45 gallon black tank. That's 135 gallons of waste water, enough capacity to hold 2 fresh water fill ups.

 

[livinthelife]

Not necessarily... it depends on the size of your tanks. On my 5er I have a 60 gallon fresh water tank, but I also have (2) 45 gallon grey tanks and a 45 gallon black tank. That's 135 gallons of waste water, enough capacity to hold 2 fresh water fill ups.

That's the same comment my husband had when I told him about this thread.

 

[hampal]

So I bought a replacement cap from Grand Design for #3 in the first picture. I'll attach another picture of the new replacement cap. How do you get the cap part off the top? It has "pull to remove" stamped on it but I'll be darned if I can separate it. I'd rather not replace the entire thing which involves removing sealant, screws, etc., from the existing flange which seems to be in good shape.

 

[trailrydr]

Here is a video of a guy replacing one.... might check it out.

https://www.youtube.com/watch?app=desktop&v=Q9Wc_SUTtgU

 

[hampal]

I did see that video already, but my vent is not broken. It looks like I should be able to just remove the cap off of the new one and snap it onto the base that's already mounted on the roof. I just can't seem to get the new cap off and I'm afraid I'm going to break it.

 

[Riverbug]

What about the symptom where trying to remove standing water from the sewer hose by walking it towards the sewer? It seems like it wants to get sucked back uphill towards the trailer.

I'm home now and went up on the roof and took a picture. If allowed I'll post it here. There are three things on the roof that look like they could be tank vents. One is white and two are black. One black one is directly above the back of the toilet and has no cap on it. Is it supposed to have a cap? The other two are capped. Nothing visibly appears to be blocked.

View attachment 51254

#1 is above the front of the shower
[URL=https://www.mygrandrv.com/forum/usertag.php?do=list&action=hash&hash=2]#2 [/URL] I have no idea what is below it but its somewhere in the bathroom
#3 is directly above the back of the toilet and I assume its the black tank vernt.

#3 has no cap. Should it have one?

Which one would be the vent for the grey tanks?

Vent #2 in your pic is a roof "vent". Don't ask me why they bother other than marketing I guess. pretty tough to vent the entire roof through that little vent especially without an inlet anywhere. Anyway, that's what that one is.

 

[jim_de_hunter]

On mine, there's a screw in hole on the top of the cap that secures the cap to the bottom. The bottom mounts to the roof.

 

[Riverbug]

I did see that video already, but my vent is not broken. It looks like I should be able to just remove the cap off of the new one and snap it onto the base that's already mounted on the roof. I just can't seem to get the new cap off and I'm afraid I'm going to break it.

As [MENTION=29895]hampal[/MENTION] said, you need to dig out the sealant from the hole in the top of the cap. There will be a screw in there (square bit) that you remove, then pull the cap off.

 

[IBEW Sparky]

So I bought a replacement cap from Grand Design for #3 in the first picture. I'll attach another picture of the new replacement cap. How do you get the cap part off the top? It has "pull to remove" stamped on it but I'll be darned if I can separate it. I'd rather not replace the entire thing which involves removing sealant, screws, etc., from the existing flange which seems to be in good shape.

View attachment 51451

Do yourself a favor and also buy a BLACK replacement roof vent and replace the white one in your picture... the white plastic gets dry an brittle and breaks easily. The black plastic has different UV inhibitors in it and will last 5x or more as long as white plastic.
I didn't need to replace the white part sealed to the roof, I just took the top cap off of the new black roof vent and swapped it with my broken white cap.

JR Products 02-29115 Mushroom Style Plumbing Vent (Black),1 Pack https://a.co/d/087bLk3Z