Evening everyone,I seem to have an issue with the gray tank venting properly, and it only occurs while taking a shower. There is a rotten stench that comes from a ceiling level kitchen cabinet, with a lesser smell coming from under the kitchen sink and from the bathroom vanity. Roof vent is clear, the under sink vents seem okay; by that I mean I took them off and the diaphragms seems to be moving freely. I don't know how to tell if they are faulty however.Don't believe the water heater is the source because I never have the smell unless showering, (hot water doesn't smell otherwise) and I use the shower daily. Diligent about flushing the water heater regularly.No dry P traps, no break in the vent pipe that I can find; I have tried all the usual suggestions I have read here previously, but I certainly could have missed something.So it was suggested to me by a neighbor that I leave the gray tank drain valve open, and voila, no smell.Anyone know why leaving the gray valve open would eliminate the smell?

Your air admittance valves in the drain lines have failed. There is one under both the kitchen and bathroom sinks somewhere. They are supposed to allow air to move in one direction-- into the drain lines when you dump the tanks, to avoid sucking the P-traps dry. But they are letting stinky gas from the gray tank in, when the gray tank space is being filled by your shower water.When you open the tank drain, that lets the displaced air go on down the drain. Right now it's burping back up through the air admittance valves.Air admittance valveIt's also likely your tank vent is plugged--either with bird or insect nest. The tank vent could also have slipped down (at the factory) and be sitting right on the bottom of the tank.

tinstartrvlr wrote:Evening everyone,I seem to have an issue with the gray tank venting properly, and it only occurs while taking a shower. There is a rotten stench that comes from a ceiling level kitchen cabinet, with a lesser smell coming from under the kitchen sink and from the bathroom vanity. Roof vent is clear, the under sink vents seem okay; by that I mean I took them off and the diaphragms seems to be moving freely. I don't know how to tell if they are faulty however.Don't believe the water heater is the source because I never have the smell unless showering, (hot water doesn't smell otherwise) and I use the shower daily. Diligent about flushing the water heater regularly.No dry P traps, no break in the vent pipe that I can find; I have tried all the usual suggestions I have read here previously, but I certainly could have missed something.So it was suggested to me by a neighbor that I leave the gray tank drain valve open, and voila, no smell.Anyone know why leaving the gray valve open would eliminate the smell?Where does your vent exit your RV? I would check and see if something maybe mud dobber, bird nest, has plugged the vent. The smell's would seam to come from the vacuum breaks. When you open the gray water dump valve you are "venting" the tank. Let us know what you find.Bill .

Double post. Isn't there some way to just dealt a post????

Like a hand of cards...once dealt...

coolmom42 wrote:Your air admittance valves in the drain lines have failed. There is one under both the kitchen and bathroom sinks somewhere. They are supposed to allow air to move in one direction-- into the drain lines when you dump the tanks, to avoid sucking the P-traps dry. But they are letting stinky gas from the gray tank in, when the gray tank space is being filled by your shower water.When you open the tank drain, that lets the displaced air go on down the drain. Right now it's burping back up through the air admittance valves.Air admittance valveIt's also likely your tank vent is plugged--either with bird or insect nest. The tank vent could also have slipped down (at the factory) and be sitting right on the bottom of the tank.Air admittance valves; that was my first thought. How do you know they have failed, other than a smell? I took both off and rinsed them out etc.; the diaphragm moves freely so I assumed they were working, but I guess not. Also, the smell is strongest in the upper kitchen cabinet, not under the sinks where the valves are...As far as the tank vent, I took the cover off and things looked clean all the way to the tank.Makes sense that the smells are going down the drain hose with the tank drain open. I guess I'll replace the air valves and see what happens. At this point I am just grateful that leaving the drain valve open gets rid of the smell! :) Thanks much for your input.

Vent issue-help me understand this | Good Sam Community

12 Replies

Katdaddy
Explorer II
Nov 25, 2017
I had this problem awhile back. Check vent tube, no problem. Replaced AAV's, still had smell when camping. Read a post about cleaning gray tank. Tried it and smell gone. Take a cup of liquid dishwasher detergent and a gallon of hot water. Put in tank before heading to campground. Dump gray tank when arrive at camp. Repeat if necessary. This worked for me. YMMV.
Ron3rd
Explorer III
Nov 22, 2017
coolmom42 wrote:
Your air admittance valves in the drain lines have failed. There is one under both the kitchen and bathroom sinks somewhere. They are supposed to allow air to move in one direction-- into the drain lines when you dump the tanks, to avoid sucking the P-traps dry. But they are letting stinky gas from the gray tank in, when the gray tank space is being filled by your shower water.

When you open the tank drain, that lets the displaced air go on down the drain. Right now it's burping back up through the air admittance valves.

Air admittance valve

It's also likely your tank vent is plugged--either with bird or insect nest. The tank vent could also have slipped down (at the factory) and be sitting right on the bottom of the tank.

While this information is correct, I recommend staying away from the cheap, $5 black ABS valves like posted in the link as they are known to leak. I recommend the Studor 20346 REDI-VENT Air Admittance Valve, $13.71 on Amazon with free shipping, $19.95 at my local Home Depot. These are residential quality and the valve inside is superior to the cheap ones. I recently replaced both of mine with the Studor valve.

Studor Valve
Dave_H_M
Explorer II
Nov 22, 2017
The Old Biscuit gave you and easy solution to isolation of the air valves. One step at a time.
j-d
Explorer II
Nov 21, 2017
I rarely get to use Full Hookups. I knew to leave the Black Tank drain closed, but thought I could leave the Gray Tank drain open. Got foul odors in coach, even with water in traps. AAV's seemed OK. Closed Gray Valve and odor stopped.
No proof, but my working theory is that the open valve allowed odor from the campground sewer system to circulate into the Gray Tank, and some of that flowed out of the Roof Vent, flooding the coach with it from the upper outside.
Old-Biscuit
Explorer III
Nov 21, 2017
Put plastic bags over AAVs.....both kitchen & Bathroom sinks
Tape them closed

Close grey tank dump valve and then take showers, use sinks etc \....see (smell) if you still are experiencing the stench

If NOT...........Replace AAVs
tinstartrvlr
Explorer
Nov 21, 2017
byronlj wrote:
Close your gray tank valve let it mostly fill and then add some bleach by pouring down the sink or shower. Let it sit for several hours and then drain. Even the gray tank gets stinky.
Dave

Good thought. Maybe the smells have built up to the point where they are obnoxious, although I still wonder how they are getting inside.

Will try sanitizing as well. Thanks.
byronlj
Explorer
Nov 21, 2017
Close your gray tank valve let it mostly fill and then add some bleach by pouring down the sink or shower. Let it sit for several hours and then drain. Even the gray tank gets stinky.
Dave
tinstartrvlr
Explorer
Nov 21, 2017
coolmom42 wrote:
Your air admittance valves in the drain lines have failed. There is one under both the kitchen and bathroom sinks somewhere. They are supposed to allow air to move in one direction-- into the drain lines when you dump the tanks, to avoid sucking the P-traps dry. But they are letting stinky gas from the gray tank in, when the gray tank space is being filled by your shower water.

When you open the tank drain, that lets the displaced air go on down the drain. Right now it's burping back up through the air admittance valves.

Air admittance valve

It's also likely your tank vent is plugged--either with bird or insect nest. The tank vent could also have slipped down (at the factory) and be sitting right on the bottom of the tank.

Air admittance valves; that was my first thought. How do you know they have failed, other than a smell? I took both off and rinsed them out etc.; the diaphragm moves freely so I assumed they were working, but I guess not.

Also, the smell is strongest in the upper kitchen cabinet, not under the sinks where the valves are...

As far as the tank vent, I took the cover off and things looked clean all the way to the tank.

Makes sense that the smells are going down the drain hose with the tank drain open. I guess I'll replace the air valves and see what happens.

At this point I am just grateful that leaving the drain valve open gets rid of the smell! :)

Thanks much for your input.
Lwiddis
Explorer II
Nov 21, 2017
Like a hand of cards...once dealt...
WILDEBILL308
Explorer II
Nov 21, 2017
Double post. Isn't there some way to just dealt a post????