Pipes Make Growling/Farting Noise At Start of Toilet Flush

[Jovannin]

We are having a plumbing noise issue for which we can’t seem to find any information or solution ideas. Hope one of you can help us out.

We have a 2008 travel trailer (Fun Finder X210) that we purchased in June. The toilet is a relatively new Dometic 310 — sticker says it was manufactured in August 2020. When we push the pedal down to flush, there is a very loud groaning/farting (raspberry!) sound coming from inside the wall. If you hold the pedal down long enough (5-10 seconds), the pitch of the sound gradually gets lower until it finally stops altogether while the toilet keeps flushing silently. If you don’t flush the toilet long enough for the noise to stop, you get the noise again for about 1-2 seconds if you flush again right away. But if you hold the flush long enough to allow the noise to stop, and then flush it again right away, there’s only a brief half-second of the noise during the flush. The noise always happens at least briefly.

The noise is worst when the toilet has been unused for a while. Not sure if there is any connection, but it also takes about 3 seconds for there to be a good flow of water into the toilet bowl. That resolves pretty much in tandem with the noise resolving.

For what it’s worth, the noise only happens when using the toilet, and it does not happen when we run water from the sink or tub taps. It happens regardless of the water source (pump and city water alike).

My husband is a very handy guy, comfortable with plumbing … but the particulars of RV plumbing are new to him. If someone can point us to exactly what we need to replace or fix, he can definitely do it. Is it a valve of some sort? Is it the vacuum breaker? Could it be the inlet on the water valve — maybe a blocked screen?

Thanks in advance!

[Jovannin]

Well, I am happy to say we’ve solved the issue, and for you all who were kind enough to reply, and for others in the future, I thought I’d let you know what we found.

Hubby checked the black tank vent as many people had recommended, using a plumbing snake, and it was totally clear. He checked the toilet plumbing and even replaced the valve (while he was correcting a bad installation of the toilet), and it was still happening. We hooked up to shore water, still happening. I listened again and decided maybe the location of the sound was actually the water heater, which is on the floor of the closet right next to the bathroom, on the side where the noises were coming from. Hubby got down and watched/listened to it while I flushed and VOILA, that’s where the noise was coming from. Seems the bypass valve that is used when winterizing had some sort of small blockage? We aren’t sure, but we had both seen a YouTube video of a guy with a plumbing noise problem in his RV who discovered that his bypass valve was not fully opened, and when he fully opened it the sound went away. Hubby had already checked that valve, but he turned the valve lever back and forth a few more times for good measure, and poof, the problem is gone. We really aren’t sure if there was a little debris in there or what, but we know there was debris in the toilet valve itself, as he replaced it and found debris in the screen.

At any rate, the horrible growl/groan/flatulence sound is gone and we can flush in peace now. Thanks, everyone, for trying to help us trouble-shoot!

[dougrainer]

There is NO code or rule that states only Toilet water goes to the Black tank. Some floorplans the design only allows the bath sink to drain to the black tank. Doug

[time2roll]

Jovannin wrote:

time2roll wrote:
Usually this would be a venting issue. Does the issue go away when the sewer drain is connected and open?

We have only had the sewer drain open twice so far and are at home now so not able to open it at the moment. What would it mean if it didn’t make the sound when the sewer drain is connected and open? Would that be indicative of a blocked vent?

Yes the open drain can provide venting for a test.

May as well get up on the roof and see if the vent cap can be removed.

[Jovannin]

dougrainer wrote:
1. Is the Line to the toilet a standard Plastic line or a flexible rubber/vinyl line?
2. Does the line if flexible go into a floor or wall opening? That line is usually either "t"d off or runs behind the wall or floor to its cold water connection point. IF flexible it could be bent/crimped inside the wall causing restriction.
3. Another cause is the toilet water line inlet has debris/calcium build up restricting the normal flow of water. To fix this you pull the toilet(easy to do) and look at the inlet and blow out if you see debris. Doug

The line to the toilet is rigid as it comes out of the wall, and then it connects to flexible vinyl line that leads directly into the toilet. If that makes any sense. So since the flexible line is only outside the wall, it can’t be crimped in there, but thank you for mentioning that. My husband pulled the toilet (because I complained about an odor) and discovered the toilet was not installed correctly, so he has just replaced the flange and gasket, and will be replacing the inlet valve tomorrow, so that should take care of any of those elements.

Interesting to note that he ran some water into the bathroom sink and saw ripples and movement in the black tank water. So we believe the bathroom sink is draining into the black tank even though people have told us it drains into the grey tank. Yet, we don’t get the noise when we run the sink, so we are not sure if the idea that it’s a blocked vent is valid, but we’ll be checking it.

[Jovannin]

time2roll wrote:
Usually this would be a venting issue. Does the issue go away when the sewer drain is connected and open?

We have only had the sewer drain open twice so far and are at home now so not able to open it at the moment. What would it mean if it didn’t make the sound when the sewer drain is connected and open? Would that be indicative of a blocked vent?

[Jovannin]

Scottiemom wrote:
Does it happen to be a macerating toilet? The one I had demonstrated to me sounds like this. In fact, the owners called it "the angry bear" because that is what it sounds like.

Dale

Thanks for sharing your idea. It is not a macerating toilet, so it can’t be that. Since several people have mentioned the possibility of it being the vent, my husband is going to check that even though he doesn’t understand why that could cause a problem. I guess he’ll find out!

[dougrainer]

1. Is the Line to the toilet a standard Plastic line or a flexible rubber/vinyl line?
2. Does the line if flexible go into a floor or wall opening? That line is usually either "t"d off or runs behind the wall or floor to its cold water connection point. IF flexible it could be bent/crimped inside the wall causing restriction.
3. Another cause is the toilet water line inlet has debris/calcium build up restricting the normal flow of water. To fix this you pull the toilet(easy to do) and look at the inlet and blow out if you see debris. Doug

[BluegrassBill]

I had a simular issue years ago. It was mud-dauber wasps plugged the roof vent pipe with mud. I cleaned and screened it, No problem since.

[time2roll]

Usually this would be a venting issue. Does the issue go away when the sewer drain is connected and open?

[Scottiemom]

Does it happen to be a macerating toilet? The one I had demonstrated to me sounds like this. In fact, the owners called it "the angry bear" because that is what it sounds like.

Dale

[bucky]

Beats the c r a p out of me.

Seriously though I would think a restricted water line is the culprit or the roof vent for the blank tank may be blocked or partially blocked.
Normally the sound you refer to would indicate a full black tank but the slow fill/flush makes me wonder.

[joebedford]

KEWL