Weird leak

[YonderAwaits]

We have a mystery leak in our bathroom. Small amount of water leaks from under the flange at the base of the drain pipe with vent on top under the bathroom sink. It seems to happen when we shower or macerate grey tanks. We removed the rubbery, hard, dark goo at the base to get a look at joint, no leak there. We replaced the vent, still leaks from under the flange. We have been full-timers for several years with our share of leaks; this one has us stumped. The location of the leak monitor is where the water appears from under the flange.
It is hard to visualize pipes under floor from basement, but no water noted under there. Thanks for any ideas!

 

[WhittleBurner]

What's on the other side of that wall? With the picture enlarged it almost looks like a slight water stain at the right corner.

 

[sande005]

You may want to call GD and ask if there should be an AAV (Air Admittance Valve) on the end of the vent. My trailer has them in same location under the kitchen sink, and in a slightly different location for the bathroom. They are typically pressed or screwed on to the pipe - not glued. Yours may have fallen off, or never been installed. That stub for a "vent" looks pretty short, and you may be getting small amounts of liquid coming out of it in the right circumstances.
The valves themselves are available at most hardware stores, which are better quality than default on a trailer.

 

[Steven@147]

@sande005 Yeah, it kind of looks like there is no AAV there.

You might try folding paper towels and wrapping it around the individual pipe joints held there by some tape, then see if one gets wet.

 

[YonderAwaits]

You may want to call GD and ask if there should be an AAV (Air Admittance Valve) on the end of the vent. My trailer has them in same location under the kitchen sink, and in a slightly different location for the bathroom. They are typically pressed or screwed on to the pipe - not glued. Yours may have fallen off, or never been installed. That stub for a "vent" looks pretty short, and you may be getting small amounts of liquid coming out of it in the right circumstances.
The valves themselves are available at most hardware stores, which are better quality than default on a trailer.

We were in the process of replacing AAV valve when I took pic, new one on now, still leaked.

 

[YonderAwaits]

@sande005 Yeah, it kind of looks like there is no AAV there.

You might try folding paper towels and wrapping it around the individual pipe joints held there by some tape, then see if one gets wet.

We were in process of changing AAV when pic taken. New one on now, still leaked. Good idea about paper towels!

 

[YonderAwaits]

What's on the other side of that wall? With the picture enlarged it almost looks like a slight water stain at the right corner.

Just a hallway, bathroom door to right.

 

[pitman44]

We have a mystery leak in our bathroom. Small amount of water leaks from under the flange at the base of the drain pipe with vent on top under the bathroom sink. It seems to happen when we shower or macerate grey tanks. We removed the rubbery, hard, dark goo at the base to get a look at joint, no leak there. We replaced the vent, still leaks from under the flange. We have been full-timers for several years with our share of leaks; this one has us stumped. The location of the leak monitor is where the water appears from under the flange.
It is hard to visualize pipes under floor from basement, but no water noted under there. Thanks for any ideas!

I see staining on top of the flange on the left side. I'd look at the back side of that pipe. If there's any water at the edge of the flange it could suck under the flange.

 

[Jbandtbone]

Check the sink for the connection to the faucet. There is some seal/gasket that dried out on mine from sitting between trips. Found these on Amazon

16435 RV Plastic Santoprene Swivel Seal 1/2" Replacement for RV Shower Freshwater Hose Pex Fittings Replace, RV Bathroom Valve fix Your leaks​