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Old 12-25-2013, 11:44 PM   #1
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plumbing vent and hepvo

howdy howdy....


im getting ready to start my waste plumbing. and am all ears looking for advice.

i am thinking outaloud or asking questions....trying to wrap my head around venting.

i am planning a single black/grey tank. the toilet will drop straight into the tank. the shower will branch onto the toilet drain as well as the kitchen sink and then head up to the roof vent.

the shower will have a hepvo valve and im neutral about the kitchen sink, ( either ptrap or hepvo).

im my reading.... i think the connection of the tiolet and shower are suspect as far as venting goes. i think code reads that there should be a vent inbetween the 2 connections. but maybe that only applies to p-traps? idk? and my other question in reading is using a common drain/vent across the width of the bus. i think i read that only works for short ~3' runs?

any expericence with hepvo?
any plumbers out there?
help !!!
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Old 12-26-2013, 09:49 PM   #2
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Re: plumbing vent and hepvo

I only have one tank due to area limitations under the bus. My toilet drops directly into the tank, and the shower and and sink also feed into that tank, with p-traps on each. I have one vent pipe that runs from that tank to the roof. No problems so far. It would be ideal to have the two separate tank, but I had to go with what I had to go with. Hope this info helps.
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Old 12-26-2013, 10:52 PM   #3
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Re: plumbing vent and hepvo

RV toilets drop directly into the black tank without an external trap. The trap is built into the toilet itself. I've never used the hepvo valve but it looks like a neat idea and looks like the easiest solution for sinks. If you use a P-trap on the sink you'll need to vent it to avoid siphoning the trap. You can either use a hard vent pipe through the roof or install a cheater vent above the P-trap under the sink. I used the cheater vent and it works fine so far. If I had it to do over again I'd use the hepvo valve and skip the venting altogether. The hepvo valves also eliminate the need to drain your traps when winterizing the bus.

Another option is to use oversized drain pipes so there isn't a plug of water going down the pipe siphoning the traps behind it. Running 1 1/4" P-trap into 2" pipe seems to work well.

Cheater vents and hepvo valves can fail (cheater vent) or clog (hepvo) and should be checked once in a while. Residential venting codes are much more stringent than RV codes(which are generally non-existent) because sewer gas can be poisonous and can actually kill you. A funky vent or trap in an RV just lets in stinky smells.

There should also be some kind of vent at the tank end to vent air as the tank fills and to vent the stink as the tank contents cook. Otherwise the gasses will pressurize the tank and will push past the trap into the RV. I only have a grey tank so I just used some 1/2" clear tubing as my vent tube with a piece of window screening taped to the end to keep bugs from taking up residence and clogging my vent.

Here's my 15 gallon grey tank with vent tube.
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Old 12-26-2013, 11:35 PM   #4
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Re: plumbing vent and hepvo

yes.... i have been looking at residential code just to be sure everything was gonna work.

i was kinda thinking that the hepvo looks like i dont need to vent. i think though that i still would have to vent the tank.... but not venting the traps will simplify the pumbing.

i think i might try 1 1/2" from the sink, straight down and y into a 2" pipe that runs across the bus into the tank.

how much do drive shafts move? it will be a tight squeeze to clear the shaft.
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Old 12-27-2013, 08:38 AM   #5
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Re: plumbing vent and hepvo

Quote:
how much do drive shafts move? it will be a tight squeeze to clear the shaft
I'm assuming you have some carrier bearings, they don't move much between the transmission and the last carrier bearing. Between the last carrier and the differential the shaft moves as much as the differential. At the transmission end it will move as much as the transmission mount lets the trans move.
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Old 12-27-2013, 09:18 AM   #6
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Re: plumbing vent and hepvo

tanks for the replies..... (rv plumbing joke)

i didnt know what those things (carrier bearings) were called, but that makes perfect sense. i will look today and see where the pipe is going to cross the drive shaft. since i am working right in front of the back wheels.... im gonna guess its the last section of drive shaft, but i'll see for sure later on. thanks for the info!!

the tank vent problem........hmmmmm
i really like the solution of not making a hole in the roof. in my first post, the tank is on one side of the bus and the vent would have been on the other side. now, if i just vent the tank.... i can keep the vent on the same side of the bus.....

but what about odors? combo tank black/grey odors?..... doesnt that little tube under the bus stink the place up? i saw another skoolie here with a pex vent placed high on the side.

my tank sits mid ship next to the entry door to the bus. the only windows in the bus are at the front and back. so i want to avoid venting near the door, back or front.....

at least i think i do
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Old 12-27-2013, 10:11 AM   #7
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Re: plumbing vent and hepvo

my vents are pex one for the black tank out the side near the top, I also have a valve on it that I can turn to let more air in when dumping but don't really need it, and my grey tank is pex vent just under the bus, also lets you know when tank is full, been 3 years no smells
scroll down the link and you will see some pictures
viewtopic.php?f=9&t=5931&start=225
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Old 12-27-2013, 11:58 AM   #8
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Re: plumbing vent and hepvo

This is a instance of where residential code is worth nothing. Code states that all plumbing fixture drains must connect with a vertical vent stack within 3 feet of the fixture. Also the vent exiting the roof must be the size of the main waste line leaving the residence.

So by that you would have to use a 3 inch vent stack leaving your bus roof. Not needed.

The small vent tube the other members are installing simply allows for volume changes inside the holding tanks as you add fluids. Water from sinks fills slowly, and unlike residential, the toilet drops directly into the black tank. This allows for a 1/2 vent tube, where as a residential house would need the 3" vent to accommodate the volume and rush of water flowing through the pipe system from the toilet. Under sizing of waste vent tube in a RV can cause your holding tanks to empty a bit slower, and cause them to burp as they are emptying.

Under sizing of a waste vent stack in a residential house can cause leaky and poorly flushing toilets, sewer gas burps from pee traps, slow draining sinks, clogged up drains from slow moving water, ect

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Old 12-27-2013, 12:20 PM   #9
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Re: plumbing vent and hepvo

thanks thanks thanks....

these are issues i know little about.... so the residential code is my starting point.

GB's bus was the pex line i was thinking of......

i ordered 2 hepvo valves today, one for sink, one for shower. as of now, im not planning on venting either fixture.

the tank vent will still take some thinking. but the smaller pex line is looking likely.
if i vented the pex to the other side of the vehicle..... that might work!

1/2" vent ? really?!?!....... i mean really??!?!
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Old 12-27-2013, 07:30 PM   #10
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Re: plumbing vent and hepvo

Quote:
Originally Posted by turf
1/2" vent ? really?!?!....... i mean really??!?!
Yup, the 1/2" vent works fine for my grey tank but the drain line is only 3/4" so the vent is probably even oversized a bit. If I had a black tank I'd have used a bigger vent since the sewage drain is a much larger diameter. Remember that going from a 1/2" vent to a 1" vent doubles the vent size but quadruples the air volume it will pass. You don't need a 3" vent for a 3" pipe. Look at the air vent on your gas cans. The air vent is way smaller than the spout diameter. Air flows through a pipe way easier than liquid does.

Some people say you need to vent black tanks up at the roof because of the smells, but I have no experience here.
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