Toilet Vent Question

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Toilet Vent Question

Postby StandUpGuy » Thu Aug 11, 2011 8:52 pm

OK this weekend I will start plumbing the bathroom of my trailer. I have established where a vent stack needs to come up for the black water tank and it will require an exposed PVC pipe in one of the corners of the small bathroom behind the toilet. Here is my question:

I have a standard 3" toilet flange for my toilet but I would like to not have a 3" pipe running up through the bathroom. Do you think it would be acceptable to reduce the vent pipe to say 2" or even 1.5"? This would not meet code in a house. But then again this is not a house. I am not venting a city sewerline.

Thoughts?
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Postby madjack » Thu Aug 11, 2011 11:23 pm

...should be no problem to use a 2 or even 1.5" pipe...are you using a RV type toilet...if so, the main purpose of the vent is to vent away sewer gas(methane), keeping your tank from exploding........
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Postby StandUpGuy » Fri Aug 12, 2011 8:03 am

I am using a roll under the trailer tank.
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Postby fromeo » Fri Aug 12, 2011 8:03 am

A standard trailer toilet configuration would be a 3" inlet on the tank for a closet flange and a 1.5" inlet on the tank for the vent.

Here's a few pics from my build. First is the bare tank before installation with the 3" and 1.5" holes drilled for the flanges

Image


And with the tank installed. To the left of the closet flange, in the wall you can see where the vent pipe will be run

Image

The vent serves a few purposes. First is obviously to vent any gases in the tank. Second is to provide a source of air for when the tank is emptied. Third, it helps prevent the traps from being sucked dry when the tank is emptied. On that third point, if you have a tank accepting multiple runs (generally on a gray tank) you will want to use air admittance valves at traps not directly off the vent stack to prevent those traps from being sucked dry.

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Postby fromeo » Fri Aug 12, 2011 8:22 am

StandUpGuy wrote:I am using a roll under the trailer tank.


Oh. Apparently I was posting while you were posting. A roll-around tank is going to be a different story then.

The only time I've seen a roll-around used in that configuration was with gray water on pop-ups. With those, the tanks are fed directly and rely on the vent built into the roll-around tank. I'm not sure that I'd be comfortable with that configuration on a toilet, that's a lot of potential odor under your trailer.

Running the closet flange into a horizontal tee to feed a vent pipe doesn't give me the warm and fuzzies either. I'd be concerned about waste backing up slightly into the vent tube causing some hard to rinse out stink.

Sorry I don't have a better answer for you.

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Postby StandUpGuy » Fri Aug 12, 2011 8:54 am

fromeo wrote:
StandUpGuy wrote:I am using a roll under the trailer tank.


Oh. Apparently I was posting while you were posting. A roll-around tank is going to be a different story then.

The only time I've seen a roll-around used in that configuration was with gray water on pop-ups. With those, the tanks are fed directly and rely on the vent built into the roll-around tank. I'm not sure that I'd be comfortable with that configuration on a toilet, that's a lot of potential odor under your trailer.

Running the closet flange into a horizontal tee to feed a vent pipe doesn't give me the warm and fuzzies either. I'd be concerned about waste backing up slightly into the vent tube causing some hard to rinse out stink.

Sorry I don't have a better answer for you.

- Frank


I imagine the vent on the roll around tank could be eliminated so there was no escaping gas under the trailer and all would travel up the vent stack. A clean out could easily be added to the stack to allow for clean out of the vent elbow. I hear what you are saying about build up in that area. Could be a problem.
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Postby StandUpGuy » Sat Aug 13, 2011 10:25 am

So is my idea of using a wheeled tank under the trailer for black water a bad idea? Is this ever done?
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Postby Tabazooron » Sat Aug 13, 2011 12:36 pm

So you're talking about using a portable tank like many use for gray water from sink?
You'd have to connect that with some sort of flexible connection because the ground to floor distance can be different on slopped sites.
Also, you'd need to do something about the tank's vent as it's normally either just an opened hose connection that would be venting gray water or some people dump their black water if they have no sewer hook-up, no "honey wagon" at the campground, and want to dump some of their black water at a dump station.
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Postby StandUpGuy » Sat Aug 13, 2011 7:27 pm

Has anybody done a set up like I am planning on doing? Will it work?
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Postby StandUpGuy » Sat Aug 13, 2011 7:39 pm

I was going to start on the plumbiong but now I am having second thoughts. Pardon the bad paint program drawing. I do not have photoshop or Illustrator on this computer. I was going to make a stack like in a house toilet situation only I was planning on reducing the stack diameter to 2". Since I do not have experience with RV toilets I am hoping someone can steer me down the correct path.


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By justoneman at 2011-08-13
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Postby madjack » Sat Aug 13, 2011 10:02 pm

...some thoughts...an RV toilet usually flushes directly into the built in tank...the vent is for pressure relief in the tank, so a vent in the trailer is not needed...a vent for the tank will be needed...if a tank similar to this is used, I believe it has a built in vent... http://www.campingworld.com/shopping/pr ... tanks/6073
...so the question I have for you...are you using a regular, low volume(a couple of quarts) RV toilet OR are you going to use a home style toilet which uses a couple of gallons to flush.........
madjack 8)
p.s. below is an "auto vent" ...it is a 1.5" vent and can be tied into the back of the "T" you show in your diagram...as long as it is above the water line in the toilet, it will do all the venting you will need(regardless of toilet type) and should be available from any box or hardware store for under 5bux...it will not vent excess pressure from tank......mj
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Postby StandUpGuy » Sun Aug 14, 2011 8:33 am

I have an RV toilet. Sounds like what I have planned is not good and that I need to rethink it.
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Postby madjack » Sun Aug 14, 2011 8:40 am

...if you are using a tank similar to the one I linked to, you can flush directly into it with setup you have drawn.......
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Postby StandUpGuy » Sun Aug 14, 2011 8:52 am

madjack wrote:...if you are using a tank similar to the one I linked to, you can flush directly into it with setup you have drawn.......
madjack 8)
That was my plan to use such a tank. My new fear based on this thread is that the waste will get lodged in the tube and not reach the tank. With the perminent type tank the waste drops directly in the tank. I imagine a liquid soup is formed in the tank and thus can be flushed out more redily. I am only guessing as I do have experience with RV toilets and tanks. Any advice is appreciated.
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Postby madjack » Sun Aug 14, 2011 9:43 am

...keep the tank as close to the toilet outlet as is feasible...I lived in a TT for several years and was generally hooked up to a central line several feet away and never had any real problems...I did run "extra" water thru the toilet on occasion to help clear the lines.........
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