tank vent help needed

[crown]

  need to put the vents in for black & gray first off all sinks and shower have p traps and [spring vents ] not sure what you call
them what i need help with is my bus is a 57 crown round roof i want to put the vent cap in center of roof to do this i would need
to use a hose or pipe that would bend to fit the curve of roof can i use 1''  and can i put a tee to conect the gray & black at the
center of roof to cut one hole and use one vent cover  where i want to put it would be  8 to 10 '' behind the a/c unit and 12 to 16 ''
in front of fantaskit vent is this ok ? or what to do thanks ps the tanks are from a monaco dyansty  1 1/2 '' size pipe

[desi arnaz]

i would put in back of the ac and the vent unless you want to smell sewer gasses

[gumpy]

I did similar to what you are talking. I installed a T at the center of the roof. I used flexible sump pump hose to connect down both sides, one to the bathroom sink drain stack, and one to the kitchen sink drain line. I'd have issues with smell, partly due to placement of the vent, and partly do to the flexible pipe not sealing properly around the barbed fittings. I placed the T in front of the rearmost roof hatch. When driving, the suction inside pulls air through the hatch seal. I've worked on the seal. I've sealed the connectors of the flex hose with teflon paste and double clamped with offset worm gear clamps. At one point I removed the T and routed the vent to the engine air intake. That sucked the traps dry. No smell while driving, but filled the coach when I'd stop and shut down the engine. I ended up using a combination of the original T roof vent and the engine intake. So far, and a year of travel, and no more smell.

1" is a bit small, but if you ran 2 of them, one up each side, and came directly off the tank, it would be sufficient for 1 1/2" drain lines.
You might find that your traps get sucked dry when you dump the tank.

craig

[PCC]

There is a product called an 'Autovent', that allows air to be drawn in to prevent siphoning, but closes the line with a spring-loaded plate when it is idle. This can be placed just a few inches above the drain level, and will keep the P-traps filled to prevent tank odor from coming back. This product is available in most hardware stores.

[Ednj]

On the Crown are your tanks under the bus?
If so why not run the vent under the bus to the back then run up.

[crown]

 i have auto vents on sinks and shower and tanks are in bay under bus right in front of rear wheels
heard if i vent out by wheels you get oders ?

[Singing Land Cruiser]

Find a local plumber with a "Heat pad". This can bend ABS or PVC to almost any fit. Some Elec Contractors carry them too. Hope this helps.  M&C

[gumpy]

Yeah, I tried those under counter vents, too. They leaked sewer gas back inside.

The problem with using those vents, is that if you place them on the sink side of the trap, the trap gets sucked dry and the gases can leak up through the trap and sink drain. If placed on the tank side of the trap where they are supposed to go, then the vent itself leaks gases.

I even tried it with the vent hooked to the engine intake, and not through the roof. The traps still got sucked dry. Not enough air could be pulled through that little vent.

Anyway, it didn't work for me.

[gus]

Those little vents work fine for me, I have two, one on each sink/shower drain line. They never leak odors, they are designed to only take in air, not let it out.

I also have under bus tank vent, never any odor problems.  This vent is 1 1/4" pvc, it needs to be larger when you dump fast, but is ok otherwise. My vent is short, since yours will be much longer you probably need at least 2" pipe.

The only time I ever have odors is when the bus sits and the traps evaporate or when I dump a full tank very fast. Then I just refill the traps and end the problem.

[PCC]

My personal experience is like Gus said; AutoVents will work until the trap evaporates enough to let air/odors pass. Make sure they are placed at a high point between the trap and the tank, and not between the trap and the sink, toilet, or shower.

They are designed to give relief air to the drain pipe and prevent a suction that takes the water from the trap.

They have a very light spring that is easily pulled, by the suction of the water flow, (easier to pull on this spring that to suck the water up from the trap), but that spring is sufficient to close off the pipe when there is no water flowing.

Keeping the trap filled is also important, as it is that water that prevents the odors from visiting with the occupants of the coach.

[Tom Y]

Crown, I ran all my drains to a common trap. I used 1" and made a trap from that also. I to ran my vent under the bus. I had 1 problem with odor when I tried to see what my top speed was. It must have blown air into my tank, because I could smell it right away.  Tom Y

[Ace]

Another one that went UNDER the bus and 5 yrs., no problems what so ever!

[bevans6]

My vent is into the rear axle bay by the previous owner, and I plan to change it before starting to use the bus in the spring.  The problem is that methane gas, highly explosive, odorless and lighter than air, will be trapped inside the tank and accumulate unless it has a natural, always rising path to vent out of.  So, andy vent that doesn't travel in an always rising path, to the outside above anything that could trap it, won't ensure that methane can vent out of your tanks.  That's the bottom line, regardless of what other things a vent needs to do.

Run your vents up to the roof.  You can do combined wet/dry vents and get rid of all those under counter Air Admittance Valves, and you can tee the black and gray together.  But it has to vent to the roof, or it's done wrong.  Sorry to be so bold.  It's just the science talking...

Brian

[crown]

thanks for all the imfo i am trying to go up to roof but what about being close to rear of a/c or a roof vent the vent would be used
maybe when showering . as we love a/c . am using 3 a/c but the mid one is more of a back up thats the one that would be close
to tank vent ?

[Sean]

thanks for all the imfo i am trying to go up to roof but what about being close to rear of a/c or a roof vent the vent would be used
maybe when showering . as we love a/c . am using 3 a/c but the mid one is more of a back up thats the one that would be close
to tank vent ?

The code says "Waste holding tank vent openings shall not be less than 3 ft (0.9 m) away from any motor-driven air intake that opens into habitable areas."

If your roof vent is exhaust-only, that's not an "intake."  However, an air conditioner may very well be considered an intake if it has provision to bring outside air into the living space.

FWIW, my A/Cs are designed principally to recirculate inside air.  For a variety of logistical reasons, one of my three units is very close to the tank vents.  I have an air flush toilet, and if that A/C unit is running when the toilet gets flushed, it's a problem, so clearly it does bring a fair amount of air in from outside.  We make sure it's shut down when using the bathroom.

If I were doing this over again, I would do whatever it took to get the tank vent at least 3' from the A/C.

HTH,

-Sean
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