Black Tank Issues Toilet Burping

[minnow101]

Thanks very much for the info. I have the same issue and I can do this myself without the trip and weeks long wait at the dealership. Just so I'm clear, it's the vent pipe that needs trimming correct?

[kozzy124]

negative ghostrider, mine was the actual toilet drain that was in to far. although it could happen with your vent pipe as well, from what I have read. it is a more common issue with the drain pipe. basically, once the level of fluid in the tank reaches the bottom of the drain pipe, that air when you flush it has to go someplace so it comes up in a burp. Its a safe bet it is your drain pipe as well.

[Cate&Rob]

Sorry guys . . . but I'm not buying this "submerged fill pipe is the problem".
You can fill any container with liquids (or solids) through a submerged fill pipe . . . if the displaced air can get out.
(I've used the analogy that you can fill a bucket with a hose placed in the bottom.)
The problem occurs when the liquid level reaches the end of the vent pipe and blocks it.
Then, the air displaced by the addition of liquid has no where else to go but "burping" back up the toilet pipe.
It's the vent pipe that's too far into the tank . . .

Rob

[kozzy124]

Sorry guys . . . but I'm not buying this "submerged fill pipe is the problem".
You can fill any container with liquids (or solids) through a submerged fill pipe . . . if the displaced air can get out.
(I've used the analogy that you can fill a bucket with a hose placed in the bottom.)
The problem occurs when the liquid level reaches the end of the vent pipe and blocks it.
Then, the air displaced by the addition of liquid has no where else to go but "burping" back up the toilet pipe.
It's the vent pipe that's too far into the tank . . .

Rob

Rob,
you are right were this can happen with the vent pipe as well, but in fact in my case it was the drain pipe for sure. my drain was confirmed 7 inches in the tank, almost touching the bottom, pipe was shortened, tank filled and drained several times by me after I got it back, problem solved. vent pipe never touched, except by me to make sure it was clear. either of the problem will give the same results, and this has been confirmed by others with the same problem and same solution. Your analogy is a little off, filling a bucket so to speak with the hose at the bottom is not the same, because the air as some place to go, the bucket is not covered.
Your toilet, is not open all the time. When the toilet valve is closed, and the liquid is at the bottom of that drain, when you flush and the valve closes, air gets trapped in that pipe, between the liquid and the toilet valve, and the liquid will still displace in the tank. That air cannot escape through the properly vented tank, because although the vent is at the correct height, at the top of the tank, the low drain pipe and the high liquid level is blocking that air from escaping from the vent. So next time you flush, that air has to go someplace, you flush, the valve opens, the pressure forces the air to release the only way it can, hence, "burps" only the air that was trapped in that pipe, all the while all the other air in the tank still vents out the correct pipe. If I could draw a diagram I would, would be easier to visualize, but I assure you it is correct.
If the vent pipe in the tank was the culprit, your toilet would have a very difficult time flushing in general, because the air cant escape, and once the vent was blocked by liquid, the toilet would not flush at all, the liquid would not go down. toilet would burp, and liquid would stay. I have seen this before in an RV toilet.....
just trying to shed some light on the situation....

[Cate&Rob]

When the toilet valve is closed, and the liquid is at the bottom of that drain, when you flush and the valve closes, air gets trapped in that pipe, between the liquid and the toilet valve, and the liquid will still displace in the tank. That air cannot escape through the properly vented tank, because although the vent is at the correct height, at the top of the tank, the low drain pipe and the high liquid level is blocking that air from escaping from the vent. So next time you flush, that air has to go someplace, you flush, the valve opens, the pressure forces the air to release the only way it can, hence, "burps" only the air that was trapped in that pipe, all the while all the other air in the tank still vents out the correct pipe.

Hi kozzy124,

I am following your logic that there was a quantity of air trapped between the closed toilet ball valve and the submerged end of the drain pipe.
I am missing how this air gets pressurized to cause a "burp". I could see how this air could be at a slight vacuum since the ball valve will close before the liquid settles to the level of the rest of the tank. Maybe the burp you encountered was actually a slight vacuum in the drain pipe under it ? The only burping that we encounter is if the tank is almost full and the vent stack is close to submerged. Definitely having the drain pipe submerged 7" into a tank that is likely little more than 7" deep, is going to be a problem. Glad you solved it . . . good info to have.

Rob

[kozzy124]

Rob,

you and I are following the same logic. I wouldn't say that the little bit of air gets pressurized a lot, but there are many variables that will cause it to just build a little pressure, since it is in a trapped enclosed space, most likely temperature. doesn't take much to give it a little burp. The liquid touching the vent stand, as in when the tank fills up, cause the same symptoms, so these 2 issues are very closely relater. This is just my logic, but I think the drain being to long is more common because of the way they install it. The drain is simply slid through a rubber grommet into the tank , and not actually attached, which would make it easy to leave the pipe to long and slide it in, while the vent pipe is cut and attached to the top of the tank with a pipe fitting and PVC cement. All this I confirmed just from trying to fix my own issue.
all good information for everyone to hopefully use if they have the same issues

[Dave and Monica]

All I can say is that I had the black tank vent pipe shortened while at the rally last year and the toilet still burps whenever the tank is more than half full. I plan to have the toilet drop pipe shortened at the rally this year.

Dave

[JWPeters]

Dave-

How is the fix (shortening the vent or toilet drop pipe) accomplished? It looks to me like the fittings are glued solid and would be difficult to remove and/or replace. Just curious if you saw how they did it.

[Paul & Deb]

Dave-

How is the fix (shortening the vent or toilet drop pipe) accomplished? It looks to me like the fittings are glued solid and would be difficult to remove and/or replace. Just curious if you saw how they did it.

I'd like to hear this answer as well plus, when you say you had it fixed at the rally what exactly does that mean? Are there service technicians hanging around the campground to work on our trailers? I had to make an appointment months ago to have my trailer worked on at the service center the day before the rally starts and they made it sound like it was next to impossible to get me squeezed in.

[RGMutchler]

At the first rally last year there were folks from Grand Design and some of the other suppliers there and they did do some warranty type work on the trailers. The work that was performed was not jobs that were extensive to my knowledge. I had the awning on our trailer fixed/repaired. I then made an appointment to take the trailer to GD's service center near the production facility and they fixed the black water tank problem. I took it to them at 6 am in the morning and was on the road before noon. GD did a very good job of trying to be attentive to customer's needs at the rally. I know several people who took their trailers to the service center for more extensive warranty issues and some told me that GD paid their lodging while the trailer was in the facility.