mystery vent?

[oldiesel]

Replacing rotted wood under the bathroom in our 78 24ft Argosy and found this vent on the pipe that runs from the shower drain around behind the grey water tank then into the top of the tank. The tank has the regular vent that is connected to the vent pipe that goes out thru the roof.Question is why is this vent on this pipe?,what could be its purpose since the regular vent is also connected to the top of the tank? i would like to get rid of it so one less hole in the floor, any opinions will be appreciated. sorry about the red picture i have no idea why that happened.

[Pahaska]

Looks like a vacuum breaker. I wonder whether it may be to prevent siphoning into the tub from the gray water tank when the trailer is on a slope.

[Aage]

It's an air admittance valve, an alternate to the regular stack, which is a pipe through the roof.

Have a look here:

air admittance valve:

https://www.google.ca/webhp?sourceid...mittance+valve

I have one on a sink in our basement, a "bar" sink, and in the 4 years we have been here it has not been a problem. However, that sink is never used. I only run it once in a while to make sure there is water in the "P" trap.

Therefore, while I can ID it, I can't comment on its workings.

[3 Dog Nite]

Our MH has one under the sink in the head. It allows air into the drain so it runs faster. It will close up so tank vapors don't come out of it. Don't eliminate it.

[oldiesel]

Aage Thanks for the link to the air admittance valve,i do also have the vent pipe out thru the roof but the info your link provided shows the valve used in conjunction with the normal vent so i guess i will not eliminate it. Don