AAV Valve for Greywater Tank?

[Tesla]

I was reading on an airstream forum about using an AAV (air intake) valve to vent greywater tanks (to avoid making roof penetrations)

Is this an adequate means of venting a ~100 gallon tank? Has anyone here had any experience with this or have any opinions? It kind of seems like it may be "too good to be true" - venting a greywater tank without going through the roof.

Appreciate your thoughts.

Sara

[chev49]

Most people will say that you have to vent at the roof, and use big vents. My first bus long ago, i used 3 inch vent for black water and 1 1/2 for grey tanks Now, on my fifth one, I used 1 inch for the black water, and 3/4 flexible line for each of the 3 grey water tanks, All are vented out the side of the bus, above the level of the plumbing fixtures. It ain't to any code, but it works fine and doesn't smell unless i go stick my nose on the exterior screen...

[lornaschinske]

AAV is a one way valve. It lets air INTO the pipes. For a waste tank, you want air to vent OUT.

[chev49]

like below the sinks...

[roach711]

What Lorna said.

The AAV lets air into the drain so the draining water doesn't siphon the trap, but it only lets air into the pipe then seals to prevent air from the tank or sewer from coming back into the room. When the drain water gets into the tank the displaced air has to go somewhere (the AAV has sealed so it can't go that way) and you need a vent at the tank.

[roach711]

Venting the drain is pretty straight forward - you either need a vent stack open to the atmosphere or an air admittance valve above the drain - not much controversy there. Venting the tank gets a bit more murky. I'm new to all this and have zero practical experience, but from what I've gathered from others on this board the rule of thumb is the nastier the smell the higher you want your vent.

My rig has only a grey tank and we will mainly be using it as a weekend warrior. My plan is to vent my 15 gal grey tank via a 1/2" tube under the bus. If I had a black tank I would be venting it through the roof or at least high on the side wall.

There are some here that have vented their black tanks down low and have reported no problems. Bottom line for me would be the difficulty involved in retrofitting a roof vent after I had all my interior work done. If I could do it easily I'd be tempted to vent down low and see how it worked out.

[Tesla]

Thanks for all your responses guys. Very helpful as usual!

Maybe we'll put an aav under one of the sinks to see if it makes a difference with drainage.

[lornaschinske]

The reasons for venting thru the roof, rather than just above the tank...

SMELLS: both the black and grey tanks can and will stink at times. Putting the vent above the roof line allows the gasses to vent above the the breeze will dissipate them and you (hopefully) don't get the lovely aroma of sewage while you are cooking/eating your burgers outside.

OVER FLOW: Some folks will neglect to dump their tanks until the grey backs up into the shower and/or the toilet won't flush because it's so full. In both cases, a tank vent that is placed at tank level could allow the contents to over flow onto the ground.

(while in a state park a family in a rental RV came over to ask me why their toilet wouldn't flush...)

BTW, AAV stands for "air ADMITTANCE valve".

[Tesla]

Yes. Air Admittance Valve. Thanks for the clarification.

[Diesel Dan]

I assume the vent pipe does not have to follow a purely vertical route? I'm thinking of routing mine up a couple inches to the bottom of the floor, then across to the side of the bus, drill a hole there and have it poke through the skirt and then run up the side of the bus to vent at the roof level. This way the only hole I have is in the side of the skirt. Granted, the vent pipe will be visible running up the side of the bus, but... ooh wait, I just had an idea ... I will need a ladder on the back of the bus for roof access anyway. I've been thinking of making it out of black iron pipe. I could connect my tank vent to the bottom of one of the ladder's vertical pipes and send the gas up that way through the ladder!

[roach711]

... ooh wait, I just had an idea ... I will need a ladder on the back of the bus for roof access anyway. I've been thinking of making it out of black iron pipe. I could connect my tank vent to the bottom of one of the ladder's vertical pipes and send the gas up that way through the ladder!

Lateral thinking at its best!

The 1/2" vent for my little 15gal grey tank will go up through the floor a foot or so, make a gentle bend so it doesn't pinch, then go back down through the floor. I just want the top of the bend to be a foot or so above the floor so the water doesn't slosh out of the vent. Will this work? I assume so, but you know what assume makes of you and me.

[chev49]

If you use small vent hose, for your vents, it might be a good idea to put a fine screen over them at the end - in case you are concerned about getting a bee nest or something in there...

As far as ladders, you can buy aluminum step plates that fold down to climb up on a boat. They cost close to a$100. If you want to make a ladder on the cheap that way, you can get some of those steel ones from one of the newer busses at the scrap yard - that flip out so you can clean your windshields, and weld something like 8 inch pads on them, and make a ladder for cheap.

[Diesel Dan]

... ooh wait, I just had an idea ... I will need a ladder on the back of the bus for roof access anyway. I've been thinking of making it out of black iron pipe. I could connect my tank vent to the bottom of one of the ladder's vertical pipes and send the gas up that way through the ladder!

Lateral thinking at its best!

Well, since my vent pipe was heading in a lateral direction, I guess my thinking just followed it to it's destination.

Whoa dude... that's like a Zen Koan or something... I think I just blew my own mind...

... but I digress...

...laterally...

...(okay, I'll stop now, I promise!)

[Tesla]

Ooh that ladder idea is slick! (wish we needed a ladder!)
=^]