What is causing this plumbing noise?

AlicePalace · 07-26-2023, 06:27 PM

We are having a plumbing noise issue for which we can’t seem to find any information or solution ideas.

We have a 2008 Fun Finder X210 (not WBS, no slide) that we purchased about 6 weeks ago. 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 — sounds like it’s between the bathroom and the wardrobe closet. 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!

**LJAZ** · 07-27-2023, 08:16 AM

Since it's only the toilet and not the sinks or tub I would think the issue might be some sort of blockage in the vent. The vent pipe from the black tank most likely is inside the wall where the noise is coming from. Try opening the black tank drain and flushing the toilet. If the noise goes away then the vent has something blocking it.

AlicePalace · 07-27-2023, 04:47 PM

Thanks, LJAZ — hubby is going to check the vent tomorrow and hopefully will be able to tell visually if something is blocking it. If not, we’ll have to try your technique next time we dump the black tank (we are currently at home working on it in our driveway, so can’t open it here).