How big does the waste tank vent hole need to be?

[ajriding]

I am repairing faulty repairs.

My gray tank is fiberglass it looks like. The vent broke right at the top of the tank. To complicate it, in order to re-install tank it needs to slide, so I cannot have much sticking out the top unless that is flexible - like a rubber pipe.

They had originally tried and failed to fiberglass the vent back to the tank.

If I were able to just put the tank straight in then I would correctly fiberglass the part back in and leave 2 feet sticking out and use a rubber boot to connect it inside the closet where it runs.

cant do this.

I am thinking to attach a flexible pipe to the tank, one that is of smaller diameter, then silp that pipe into the vent stack pipe far enough up that water/waste will not slosh up and over and back down into the camper.

1. How high? Tank is side-to-side and vent is front corner of the side.

2. How large of diameter pipe is good enough to have regular waste disposal flow?

[ajriding]

Rvpapa wrote:
Glass in a threaded hub on the tank. Cut off a section of vent stack in closet. Install male threaded end on cut-off. Trim to appropriate length. Screw into tank using sealer on threads. Join to stack with M-J clamp.
Art

That's why I come to the forum. Sounds perfect, thanks.

threaded pvc fitting, fiberglassed in. Little messy, but does the job.
This is actually better than original since it can be removed without cutting or breaking if tank needs to come back out.

[Rvpapa]

Glass in a threaded hub on the tank. Cut off a section of vent stack in closet. Install male threaded end on cut-off. Trim to appropriate length. Screw into tank using sealer on threads. Join to stack with M-J clamp.
Art

[ajriding]

time2roll wrote:
Yes and I am thinking gas will move faster than water so I would be looking at 1" or 3/4" if absolutely necessary. Maybe 1/2" but that has a much greater chance of creating issues. I assume code is 1.5".

Yes.

Air flows easier than water, so pipes do not need to match. I don't plan on putting water in the tank (shower, sink, flush) fast, just to drain it out fast.

My tank is over 1/4 inch thick at vent (black outer layer and white, smoother, inner layer), would this grommet fit? It looks to be made for a thinner wall.

the grommet sounds perfect, except I absolutely can never, ever have a leak on the camper floor. I just spent a month cutting out the fiberglass floor, pulling out soggy wood and installing new floor and new fiberglass patches. The grommet would stick through the floor or not? If I put that one in link upsidedown it might work. I never fill tanks, so not worried about an inch loss.

[time2roll]

Yes and I am thinking gas will move faster than water so I would be looking at 1" or 3/4" if absolutely necessary. Maybe 1/2" but that has a much greater chance of creating issues. I assume code is 1.5"
Be careful how easy that flexible line can restrict flow as it bends.

[Nv_Guy]

As Joe417 said, there are rubber grommets that allow you to push the vent pipe down into the grommet. Only issue is you wont have a perfect watertight seal, so you don't want to fill the tank past full. The grommet does have a "stop" molded into it, but you can push past it. So you have to make sure not to push the vent pipe to far into the grommet as that wont let the tank get to full capacity. .

Grommet link

[Old-Biscuit]

Drain line to tank is 1 1/4" so Vent line from tank needs to be same/larger size

In order for water to flow in to tank...air has to be expelled from tank at same rate

[Joe417]

I have a '01 5th wheel and an '05 TC and both have a sliding vent. There is a rubber grommet that is all most flush with the top of the tank and is sealed into the tank with some type of putty.

The vent pipe is pushed into the rubber grommet after the tank is in place and then mounted to the campers. This allows the pipe to move up and down as the camper flexes.

I can't remember the exact size, 1.25 or 1.5 inches.