Answers to questions about RV repair and maintenance from RV expert Dave Solberg, managing editor of the RV Repair Club. This column appears Monday through Saturday in the RV Travel and RV Daily Tips newsletters. (Sign up for an email reminder for each new issue if you do not already receive one.) Today he talks about gurgling drain pipes.
I have a 2010 Damon Avanti which has been a great rig. I am having a problem with the plumbing. When I have the gray water valve shut I get gurgling noises from the drain pipes, especially when running a sinkful of water through either sink. It all works fine when the valve is open.
I have done the baking soda/vinegar trick in both sinks and the shower to unclog any obstructions. I have replaced the air vents under both the kitchen and bathroom sinks. And I just replaced both roof vents with 360 Siphon Vents. Replacing the roof vents helped, but did not solve the problem totally. Any ideas on what is going on or what else I may try? —Laurie
All tanks in an RV need to be vented such as the fresh water, black water, and gray water tanks. They start out full of air and as the water or waste enters and starts filling the tank the air needs to go somewhere and that is designed through some type of vent. If not properly vented, the air pushes back up the drain pipe in the case of black and gray water tanks, or full tube of a fresh water tank. This will cause a gurgle or bubble back up the pipe as it is being filled or will stop filling/draining completely and cause backflow.
The best solution to vent a tank
The best solution for venting a tank is to run a 2” PVC pipe from the top of the tank to the roof and put a cap over it. This allows maximum air flow that can match the volume of water going into the tank.
You indicated that both roof vent covers or caps were replaced with the 360 Siphon and this helped. This would indicate that the old vent cap might have been plugged, somewhat restricting the venting. It could also mean the vent design of your rig was not sufficient for the amount of water volume going into your gray water tank. Has this happened from the start or just started? If it is from the start, it could be a design issue. If it just started, it would be an issue with a plugged vent somewhere.
“Cheater vents” under the sinks
You also indicated you changed the air vents under the kitchen and bathroom sinks. These are commonly referred to as “cheater vents” because the vent comes up from the tank. Since there is an open countertop it cannot go all the way up to the roof. So manufacturers bring the vent tube up a couple of feet and put on a cap that allows air to come in, but restricts the odors from emitting out. These are a constant issue as they not only allow odors to come into the coach but also create too much resistance for venting.
I would suggest removing the cap from under the sink or bathroom and draining the sink to see if that eliminates the gurgling – which I believe it will. If you bought the replacement “cheater vent” cap from a home improvement store, it would be designed for residential applications and might have a higher pressure. You would need to get a cap for an RV application.
If the problem is still present, then I believe it’s a design issue with a vent pipe that has a sharp 90-degree bend that restricts the air flow.
Read more from Dave here.
Dave Solberg worked at Winnebago for 15 years developing the dealer training program, as marketing manager, and conducting shows. As the owner of Passport Media Creations, Dave has developed several RV dealer training programs, the RV Safety Training program for The Recreation Vehicle Safety and Education Foundation, and the accredited RV Driving Safety program being conducted at rallies and shows around the country. Dave is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club.
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