Bathtub Won’t Drain

[MyDog’sRV]

I have an issue where my bathtub wouldn’t drain and it turned out to be the air admittance valve for the kitchen sink. It is the only AAV in our small trailer and affected the tub since the sink drain line joins the bathtub drain line before proceeding to the gray tank. The AAV was hard to find too. It was located in an inaccessible area between the microwave compartment and the under the sink compartment. I discovered it by using a $20 endoscope camera hooked up to my laptop and shoving it up into that space from the cupboard below. I had to remove the microwave and knock out a cabinet wall to get to the AAV. I reached up in there and when I unscrewed the AAV I heard a whooshing sound as the bathtub suddenly drained! I will add that the drain line from the bathtub to the gray tank is quite long and has 4 90 degree elbows and at one point it runs uphill before exiting. It is so tight under there that instead of a p trap there is a special pinch valve trap. I might add that at the time my trailer wasn’t sitting level and was tilted away from the gray tank connection but did not matter.

 

[SpencerPJ]

Good post with pictures, thx. Glad you found and corrected your problem.

 

[Rene T]

And welcome to the forum

 

[MyDog’sRV]

Good post with pictures, thx. Glad you found and corrected your problem.

Unfortunately when I installed the new valve the bathtub does not drain until I remove the vent. I did figure out that when I remove the vent air is coming out of the tube it is installed in. I guess the issue is that the gray tank isn’t vented properly.
The vent tube actual is exposed in my bathroom so I can touch it. I pulled up on it slightly and the tub gurgled and a little water drained out of the tub. I’m afraid to do anything more than that. Might need a professional to raise the bottom of the tube in the tank. I was tempted to just pull it up from inside the bathroom but I don’t know if I might ruin the seal on the top of the tank or the roof seal.

 

[Viajeros]

Great post. We had something similar happen to us and kinda figured it out by fluke.

Thanks.

 

[Henry J Fate]

Typically an AAV has nothing to do with normal drainage from appliances. If an appliance has a drain problem, it will either be a blockage in the line or a blocked tank vent. Tank vents will block up when off level depending on the design and how full the tank is and dumping the tank can easily exceed the abilities of tank vents which is primarily when the AAV does its job. The AAV prevents the water in appliance traps from being sucked out thus keeping foul and sometimes volatile odors from backing into the RV. The AAV won't open during normal appliance usage and is not designed to do so. If an AAV opens during normal use, there is a problem with the plumbing or possibly an unlikely bad AAV.

 

[Domo]

Is the gray tank vent pipe blocked on the roof?