Sewer Odor (most likely the grey tank)

I have noticed if I drive with a near full grey tank that the sloshing around in the tank will push and pull the water from the p-traps and then the smell begins.

I had a similar problem -- discovered that the washer drain hose extended too far into the drain, displacing the water in the P trap, allowing the sewer gases to come into the living area. Solution was to raise and secure the washer drain hose so that it only extended 1 to 1 1/2 inches into the drain, allowing the water in the P trap to do it's job of blocking the sewer gases.

bshpilot wrote:
i understand what the AAV is and how it works - i don't understand why builders complicated the system and moved away from a roof vent.

Because it is easier for them. Take your sink, if you wanted to vent it to the roof.

Since the RV only has 2by2's you really could not go horizontal with the vent stack (tying it in with the existing one) without structural weakening of the walls. Which now means you must go threw the roof with another vent stack.

The more holes you got the more chance of leaks you have. Also from the makers point of view they would have to pay someone to put all of that together and buy the parts for it. An AAV is about $5 and takes one minute to create the plumbing for it.

Trick to the AAV is if you do replace it put a little bit of Vaseline on the threads prior to screwing the new one on. Next guy will appreciate it.

On edit:

Also just hand tighten it. Most the time it is impossible to get a wrench in there, and hand tighten is all it really needs.

I can only add: Check the vacuum breakers under the sinks. They might be stuck open allowing fumes inside the coach. It is nothing more than a rubber flap valve, and it can get dirty, and stick open. Check it and see.

i understand what the AAV is and how it works - i don't understand why builders complicated the system and moved away from a roof vent.

bshpilot wrote:
silly question:

whats up w/ the Air Admittance Valves ? whats the design/thought behind them ?

The valve is nothing more then a check valve, but for air not water. It allows air to enter, but not escape. When they do go bad, they allow air to escape and, in this case the air ( really gas) will be from the gray tank.

For a drain pipe to work correctly it must not be more then half full of water. When it goes past half it requires outside air (behind it) to help it flow. If it can't get it, it will create a suction. In this case it created a suction and pulled air threw the washer drain pipe.

To save money not all drains are vented to the outside (due to cost and accessibility.) So the cheap and easy solution is to use one of those AAV's instead of a vent stack to the roof.

So that is the theory why some of us think it's the AAV. Could be something else of course, but the fact that it gurgled in the washer pipe is key.

thomkatt wrote:
I was having black tank smells even with Enzymes in the tank. Got one of those directional flow units and put it on the top of the vent, NO MORE SMELLS!

Directional flow units work good because it sucks all the odor from the tanks creating a venturi effect. But the suction effect still does not break down solids and on the grey tank it still does not clean the walls inside the tank from grim off dishes that stick to the walls. Enzymes and there are different brands are recommended by most RV parks. They even sell the stuff at Thousand Trails RV resorts.

That is why so many have problems with the reading of the tank gauges because of the sludge that has accumulated on the walls of the grey tanks, and toilet tissue on the black tanks.

But if the directional unit works for you? The more power to you. I installed one on my coach also when I first bought the unit.

I was having black tank smells even with Enzymes in the tank. Got one of those directional flow units and put it on the top of the vent, NO MORE SMELLS!

Thanks for all the advice! I think I will try replacing all three of the mechanical vents and if I still have problems then I will route one or all the vents as suggested in a PM by Pangaea Ron.

ljr869 wrote:
Odors can sometimes come out the grey tank roof vent and then into a kitchen or other fresh air roof vent.

no doubt !

Ive always been told not to open the (roof) vent / fan especially in the water closet if the fan isn't running in EXHAUST (out) mode.

silly question:

whats up w/ the Air Admittance Valves ? whats the design/thought behind them ?
I could see it for a "clean" roof on coaches that have basement air conditioning...but from what I'm hearing here, the AAV's seem to be a problem & maintenance area.

the tank vent "stacks" on my coach aren't really even visible on my roof...im trying to understand what the advantage is behind the AAV's.