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Old 12-31-2013, 08:08 PM   #1
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Drain Line Vent Questions for Experienced Plumbers

I need some advice again. I am re-plumbing the drains in my 66 Trade Wind. I have new black and gray holding tanks. My trailer has THREE vent pipes through the roof. Leak, leak, leak! My 86 has TWO, one for each tank. Only the tanks are vented in the 86.

Okay, the kitchen sink will run over the wheel well, tee to the vent pipe, and drain into the gray tank on the street side, close to the dump port. Should be okay.

The shower drain will tee into a vent line on the curb side, and drain into the gray tank on the curb side, opposite the dump port. Should be okay.

The bath sink will drain into the BLACK tank on the crub side. The toilet will drain into the black tank on the street side. The single vent for this tank is also on the street side.

Will the bath sink drain okay with a vent clear on the other side of the tank? I'm using 1 1/2 inch ABS pipe.

I'm wanting to do it this way so I can expand my gray water capacity a little bit. Toothpaste and hand soap in the black tank shouldn't hurt a thing. Extra water in the black tank helps it rinse clean.

Will this vent system for the bath sink drain work okay in your experience?

David
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Old 12-31-2013, 08:24 PM   #2
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Your bathroom sink will probably drain slow, and the kitchen sink might as well depending on how long the run is to the tank vent line. The vents are not only to vent the tanks, but also to allow air into the drain after the trap to help water flow down the waste system properly. I suggest that you install air-admittance valves under for the bathroom sink, and maybe the kitchen sink as well. We did at both the bathroom sink and kitchen sink, and they work great.

Here's a link to our thread. http://www.airforums.com/forums/f185...-50967-23.html Post 311 shows the plumbing under the bathroom sink. The air admittance valve is the cap-like thing sticking straight up behind the trap.



Chris
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Old 12-31-2013, 10:00 PM   #3
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David
We also used the air admittance valve at the kitchen sink. Work great! Got it at the local hardware store.
Tim
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Old 01-01-2014, 06:18 AM   #4
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Thank you for your advice Chris and Tim. Chris, I have read your post end to end. It is very informative and the cabinets you and Kay created for your Airstream are fabulous! I also admire your electrical / electronic knowledge.

The kitchen sink drain vent is about 3 feet from the trap, and it will stay original. The new shower vent will be about 2 feet from the trap. I will use an air emitter valve for the bath sink just after the trap so the drain line can breath. I hope they are sensitive enough so they don't let any fumes out of the "sewer".

I just didn't know if the air pressure in the drain lines would equalize with the vent way downstream in the tank itself. I wouldn't expect the water flow to take anymore than half the diameter of the inside of the pipe.

Must the air emitter valve be higher than the trap?

David

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Old 01-01-2014, 06:45 AM   #5
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Having the kitchen skin tee-d into the vent pipe is a known issue in the newer front bed trailers.

If one dumps a sink full of water at once, the slug of water occludes the vent and air being displaced from the tank vents out the shower drain. If the tank is close to full, a bit of smelly water will make into the shower floor.

Just a thought.

Regards,

JD
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Old 01-01-2014, 09:17 AM   #6
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3 things all plumbers need to know... Stuff runs downhill. Wash hands before eating. Payday is Friday.

Since I don't know what you know, I will take a stab at it.

Use p trap to block odors and gas from tank backing into the sink. Liquids and anything in sink drain will pass the trap then enter piping. The piping should slope down toward tank about 1/4" drop Per foot of run. This will give a good drop even when trailer is slightly unlevel.

If the run is too far you may need air vent near the p trap on the tank side. That way the vent air doesn't have to make its way in from tank where there is more stink or getting full.

Some tests with food colored water should give a good idea of flow.

Oh, also you want the piping to drain so that when you slam on brakes or aim the trailer nose downhill there won't be a slug of waste water in the long drain pipe to fill up your sink.
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Old 01-01-2014, 01:15 PM   #7
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Hi David,

Yes, the air admittance valve needs to be higher than the trap. Put it as high as possible under the counter, but leave room to remove it in case you need to replace it. The ones I have screw onto the drain pipe. Inside, they have a rubber one-way valve that does block all sewer gasses from coming into the trailer from the tanks. But, like everything made of rubber, it'll eventually wear out and need to be replaced. No idea how long that'll take though. We had these valves on previous SOB trailers for many years without any issues.

I think you should add one under the kitchen sink. They're cheap and fairly easy to install, and will ensure that you don't have a slow drain or venting issues.

Chris
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Old 01-01-2014, 07:29 PM   #8
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Okay, will do. Keep the potbelly stove hot on these very cold nights! David
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