Tank vents

[msnglinc]

Can the vents from the black tank and grey tank be combined before exiting through the roof? Can the grey vent just be from the sink drain like a residential system or does it need to come from the tank itself? If it comes from the tank do I need one at the sink as well?

[MtnDon]

Can the grey vent just be from the sink drain like a residential system or does it need to come from the tank itself?

If the tank that the sink drains into does not have its own vent the tank may build up air pressure, or there may be gurgling. Also w/o a tank vent the tank may not be easy to drain. Air needs to move in and out of the tank as water enters or leaves the tank.

As for combining black vent with grey vent I think as long as the vent to vent crossover/coupling is high enough to ensure there would be no mixing of the waste waters it would be okay. My last commercially built RV had one vent for each though.

If it comes from the tank do I need one at the sink as well?

In a residence the plumbing code permits a distance of 5 feet from sink drain to vent when using a 1-1/4" pipe, 6 feet with 1-1/2" pipe. That is mainly to promote gurgle free draining and prevent water suction from pulling water from the p-trap.

[flboy]

Why don't you just use an Air Admittance valve under the sink or where ever your closet point in the drain line system is near the Gray Water tanks (after all the the traps). My understanding is that these valves are one way and will pull air when the tank is drained, but not vent the tank into the living area. I am going to give this a try on my system as I really do not want to run another vent through the ceiling. The vent I bought does not look like this one, but it gives you a general idea of what they look like.

[msnglinc]

Thanks Don. The combined will be plenty high enough so that won't be an issue. Gonna have to rethink my routing to get both a tank and sink drain vent in there.

[McDave]

Hepvo, Hepvo, Hepvo......http://www.hepvo.com/

McDave

[Iconfabul8]

Air Admittance valves Won't work on a tank system. Like MtnDon says air has to be able to escape the tank as water goes in.

[hankaye]

Iconfabul8, Howdy;

Air Admittance valves Won't work on a tank system. Like MtnDon says air has to be able to escape the tank as water goes in.

NOT to be argumentative, but if the AAV (Air Admittance Valve), doesn't work on a tank system
then why do I have one in the Galley drain system under my kitchen sink? I live in an RV and even
the prior RV even had an AAV for the tub/shower drain. Never have had any problems with them
at all ... and that includes smells haven't had one burp back at me yet ... knock on wood.
Mine looks like this;
http://www.lowes.com/pd/Keeney-Mfg-Co-1 ... nt/1069119

hank

[Iconfabul8]

I admit I don't have any practical experience. Just using logic, knowing as the water enters the tank, the air has to be going somewhere. What do you think is happening? I'm here to learn!

[cdub]

Why don't you just use an Air Admittance valve under the sink or where ever your closet point in the drain line system is near the Gray Water tanks (after all the the traps). My understanding is that these valves are one way and will pull air when the tank is drained, but not vent the tank into the living area. I am going to give this a try on my system as I really do not want to run another vent through the ceiling. The vent I bought does not look like this one, but it gives you a general idea of what they look like.

I used similar on my sink drain but you still need a vent in the tank as well. The one way is for draining the sink and drawing air in, but when the tank fills with water the air needs to be dispersed and the valve prevents this by design therfore building pressure and prevent drain.

[flboy]

Good point. I'll figure something out for that without another pipe... I'd think with the size of the tank and the relatively small amount of water flowing in at any given time, all I need is a small hole.

Sent from my SM-N900P using Tapatalk

[msnglinc]

With a 1 1/4 inch drain line and the fact that its just a gravity drain wouldn't there be enough space in the pipe for water to flow down the hill to the tank on the bottom 1/3 to 2/3's of the pipe and air to flow back up the pipe in the top 1/3, kinda like a two way street? Does that explanation make sense? Since it's not under pressure I doubt that size of pipe would be full under normal drain conditions.

[MtnDon]

The water / air still has to pass through the p-trap. Gurgle, gurgle, or at worst nothing moves at all.

[hankaye]

Howdy All;

AAVs are akin to taking your finger off the end of a straw full of liquid and are designed to be
installed downstream from the trap. Allows the air to infiltrate to prevent the gurgling and
will also allow the line to drain when the dump valve is opened. My galley tank is separate from the
others in my RV and has no roof vent, The drain line is 1.5" and is only connected to the rest of
the drains at the hub where the drain hose is attached about 10 to 12 feet from the tank. Never a
gurgle, never a problem. Only has an AAV like the one I linked to earlier just downstream from the
under sink trap in the cabinet under the sink. So, I'm just speaking from experience.

EDIT: Here is a DIY link explaining the install of an AAV:
http://www.diyadvice.com/diy/plumbing/k ... nce-valve/

hank

[msnglinc]

The water / air still has to pass through the p-trap. Gurgle, gurgle, or at worst nothing moves at all.

I would place the vent just after the P Trap.

[McDave]

Well, let's try this.
1.) Small fitting say 3/8" threaded into grey tank at or near top with hose connected to 2nd 3/8" fitting threaded into existing vent pipe well above "liquid" level. This allows air to escape/displace from grey tank while sink/shower is draining.

2.) Hepvo Valve (can you tell I like these things?) in place of P-trap. It acts as a 1 way valve preventing gasses from coming up from tank, while letting fluids AND gasses (air) enter pipe during drain/ tank empty cycle. Now for the bonus....THEY WONT DRY OUT DURING PERIODS OF NON-USE, OR FREEZE, OR ALLOW BACK UPS, THUS PREVENTING STINKY RV SYNDROME.
They also take up a lot less space and allow for installation with out building a raised floor for shower etc. etc.
http://www.hepvo.com/


Just sayin',

McDave