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Old 12-25-2013, 10:44 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, 08:49 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, 09:52 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, 10:35 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, 07:38 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, 08:18 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, 09:11 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, 10:58 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

Nat
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Old 12-27-2013, 11:20 AM   #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, 06:30 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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Old 12-27-2013, 06:57 PM   #11
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Re: plumbing vent and hepvo

I have not had any smells from my black tank vent, and it drains out fast using the 3 inch slinky, the grey water is fast as well, never had a problem dumping the tanks,and best of all no holes in roof
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Old 12-28-2013, 10:04 AM   #12
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Re: plumbing vent and hepvo

I'm thinking the hepvo valves would work as well passing air to the tank as they do water so you'd only need a small vent at the tank. When you dump the tank the hepvos (presumably) would open up and provide basically a 1 1/4" one way vent.
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Old 12-28-2013, 01:39 PM   #13
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Re: plumbing vent and hepvo

Quote:
Originally Posted by roach711
I'm thinking the hepvo valves would work as well passing air to the tank as they do water so you'd only need a small vent at the tank. When you dump the tank the hepvos (presumably) would open up and provide basically a 1 1/4" one way vent.
Hepvo valves do not allow air to pass through. If they did, they would not work for what they were invented for. The vent needs air to pass freely both ways.


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Old 12-28-2013, 07:20 PM   #14
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Re: plumbing vent and hepvo

Quote:
Originally Posted by nat_ster
Hepvo valves do not allow air to pass through. If they did, they would not work for what they were invented for. The vent needs air to pass freely both ways.
Admittedly, I have no personal experience with the product, but the design suggests that it would have to pass some air toward the tank once the water drained through the valve.

Imagine a slug of water going down the drain pipe pushing air ahead of it into the tank and also pulling air behind it from the sink. The water column would draw air through the hepvo and the tank vent would vent the pressurized air going into the tank. Once the water column settles in the tank the hepvo would close keeping water and air from coming back into the sink.

The tank vent needs to pass air both ways because the tank will be both filled and drained. The sink drain requires that air flows only toward the tank. A cheater vent and, presumably, the hepvo valves pass air only toward the tank.

So, at least theoretically, I stand by my suggestion. The small tank vent would handle the small air volumes from showers and sinks draining but may be too small to efficiently dump a black tank through a 3" drain line. In that case there would be a negative pressure in the entire drain system which (may) open the hepvo valve and provide additional tank venting.
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Old 12-28-2013, 08:47 PM   #15
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Re: plumbing vent and hepvo

roach711
I hear what your saying about the small vent on the black tank, I have a 1/2 pex vent on my 30 gals black tank, and it dumps just fine , no problems at all
its all good
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Old 12-28-2013, 09:17 PM   #16
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Re: plumbing vent and hepvo

Thanx GB. We can argue theory and "what should work" all day long, but nothing beats the guy who comes along and says "I did it this way and it worked just fine."
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Old 12-28-2013, 10:33 PM   #17
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Re: plumbing vent and hepvo

Quote:
Originally Posted by roach711
Quote:
Originally Posted by nat_ster
Hepvo valves do not allow air to pass through. If they did, they would not work for what they were invented for. The vent needs air to pass freely both ways.
Admittedly, I have no personal experience with the product, but the design suggests that it would have to pass some air toward the tank once the water drained through the valve.

Imagine a slug of water going down the drain pipe pushing air ahead of it into the tank and also pulling air behind it from the sink. The water column would draw air through the hepvo and the tank vent would vent the pressurized air going into the tank. Once the water column settles in the tank the hepvo would close keeping water and air from coming back into the sink.

The tank vent needs to pass air both ways because the tank will be both filled and drained. The sink drain requires that air flows only toward the tank. A cheater vent and, presumably, the hepvo valves pass air only toward the tank.

So, at least theoretically, I stand by my suggestion. The small tank vent would handle the small air volumes from showers and sinks draining but may be too small to efficiently dump a black tank through a 3" drain line. In that case there would be a negative pressure in the entire drain system which (may) open the hepvo valve and provide additional tank venting.
Well worded description of the system and your point.

If it ever douse start chugging at the waste dump, anyone could just open their toilet to release the suction. Might speed up the dump even if your not having problems.

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Old 12-29-2013, 07:16 AM   #18
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Re: plumbing vent and hepvo

This is my next project...a porcelain throne, I am using a low water unit modified for even less water

Do I really need a 3 inch vent?

I don't read codes....or I wouldn't of guided the 2 prong plug into wall with my finger
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Old 12-29-2013, 11:06 AM   #19
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Re: plumbing vent and hepvo

Quote:
Originally Posted by nat_ster
If it ever douse start chugging at the waste dump, anyone could just open their toilet to release the suction. Might speed up the dump even if your not having problems.

Nat
Another good point. Just shows there's more than one way to skin a cat.

Bansil - GBStewart says his black tank has a 3" dump drain and a 1/2" PEX vent and drains without "glugging."

I believe the electrical code pretty much leaves the the plugging in of cords up to us to figure out (and, for the record, you aren't the only on who's figured out the wrong way to plug in).
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Old 12-29-2013, 01:19 PM   #20
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Re: plumbing vent and hepvo

Quote:
Originally Posted by bansil
This is my next project...a porcelain throne, I am using a low water unit modified for even less water

Do I really need a 3 inch vent?

I don't read codes....or I wouldn't of guided the 2 prong plug into wall with my finger
bansil

Because you will be using a regular residential toilet that need the massive volume change to induce the flushing, You may need a bigger vent line. To make this even more challenging, reducing the amount of flush water will make the flush less powerfull.

In the cabin I built last summer, I used a 1.5 inch waste vent pipe. It flushes well as long as you wait 30 seconds between flushes, so the big 3" drain line can clear the bubble. Your bus should do just as well, if not better. Your toilet will drop directly into your tank. The cabin has 8 feet of 3" drain pipe to pass through.

Nat
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