Hepvo trap for the 400 shower (not for the faint-of-heart)

rh5555

Do you sometimes get evil smells emanating from your shower drain?  Particularly after driving down some bumpy roads?  It's because the water in the u-trap under your shower pan gets shaken out and then allows grey water fumes to enter your bathroom.  Our standard fix was to pour a cup of water down the drain to re-fill the u-trap.  But what's the fun in that?

This mod solves that problem and also will stop the grey water tank backing up into your shower pan:  Remove the u-trap and replace it with a Hepvo trap.

Warning:  This is far and away the most awkward mod I've made to the trailer.  Access is awful and you can barely see what you're doing.

Anyway this is what it looks like to start with:

Removing the rubber U-trap is easy - just unscrew the fitting from the shower drain and loosen the hose clamp that clamps the utrap to the 90 degree bend.  Water in the U-trap will spill all over.

Next, you need to cut through the (vertical) riser about 3/8" above the floor level.  I cut the horizontal pipe first because the 90 degree bend got in the way of my saw.  Clean up the cut pipe to remove any burrs.

Now you have to assemble the Hepvo trap and associated ABS fittings.  Sorry that I don't have pictures of this bit, but I was a little flustered at the time.  What you need is (in order from the shower to the riser):

1. The right-angle connector that comes with the Hepvo trap
2. The Hepvo trap itself
3. A 5" length of 1.5" white PVC tube (I cut mine from one of these)
4. An 2" ABS compression fitting
5. A 2" ABS street Ell

Start by gluing item 4 to item 5.  Then assemble them all to do a dry fit.  You need to get the length just right (the components slide in and out to make this easy) by pushing item 5 onto the riser and screwing item 1 into the shower drain.  Tighten all the compression fittings and remove.  Now comes the really hairy bit:  Apply ABS cement to the open end of item 5, then reach in and push it onto the riser (which you can't see) while aligning Item 1 with the shower drain (which you can now tighten up).  If all went well, it will now look like this:

and

There are 2 styles of Hepvo trap on the market.  They only differ in the size of pipe that enters the trap.  Since we're not using those bits, you can use either size.

Sharon_is_SAM

If the valve prevents backup into the shower pan, where does the water overflow in the event of an over filled gray tank?

Horigan

Assuming the valve is truly water tight, the water would emerge from either the bathroom or kitchen sink, which ever is lower.  I suspect though that water would initially fill up the sink drains, then slowly leak through the Hepvo valve into the shower.

Denny16

On rh555’s 2020 TaB 400, the galley (kitchen) sink also has a factory installed Hepvo, so the only place for a backup to drain from is the washroom sink.  The next exit point is the gray tank vent pipe on the roof.  Not sure if the 2020/2021 has an overflow on the top of the gray tank, which would prevent a backup in the trailer.  The 2018/2019 does not.

I do not have a washroom sink, I installed a Hepvo trap valve in our galley sink, and if I did this mod to the shower (So I could plug the hole in the trailer bottom), then the only place an overflow would have to drain from on our 2018, is the roof vent pipe.
So at this point, going to give this mod a pass. 
cheers

rh5555

On the other hand @Denny16, you would absolutely know when your grey tank was full because your sink(s)  wouldn't drain.  Isn't that better than doing the washing up and then finding grey water in the shower?  That was our thinking...

Denny16

Good point, you are correct it would.  @rh5555 Did you notice if the hole in the floor under the J/P/U trap was cut all the way through?  Shower is quick to clean, it’s gray water, not black water, so a good rinse cleans it right up.
cheers

rh5555

Our hole had duct tape covering it up from underneath.  I intend to fill the hole with some expanding foam.

Denny16

Thanks, and a good idea.  I want to do the same, another entry point for rodents, and other creepy crawlers that go bump in the night. 
cheers

Verna

@rh5555, there is an expanding foam that has a rodent repellent substance in it that would be good to use. Think about placing copper screening material in the hole and then the expanding foam, just in case the rodents decide they like the anti-rodent substance.!

Denny16

Excellent suggestion Verna, thanks.
cheers

TNOutback

@rh5555 you are either brave or crazy for doing that mod! . How in the world did you get the pipe cut?

@Sharon_is_SAM I can attest to the fact (more than once) that the 2020 400 has a vent on the top of the gray tank which will spill water if you overfill it.

Another benefit of this mod is that you eliminate a possible freeze up issue in the winter and would no longer need to put antifreeze down that drain.

Sharon_is_SAM

@TNOutback - is that gray tank vent visible or is it under the corroplast?

Denny16

Sharon, TNOutback stated the vent is on top of the gray tank.  The tank is in between the frames and covered by the corroplast.  You would need to remove the corroplast to see it, I do not think it has a tube attached to it like the fresh water tank vent/overfill drain. 

Both the black water and gray water tanks are naturally aspirated (vented to the atmosphere).  From the photos I have seen, both tanks are connected to a single vent pipe, coming out the roof (runs in back of closet area wall on TaB400).  I have not seen a second overfill drain/vent on top of either tank in the construction photos previously posted here.  The gray tank vent connection is on top of the tank.

The overflow leak coming out the corroplast panel seen by some new TaB owners, may be the result of a poor connection between the vent pipe to tank connection on top of the gray water tank?  I would think a purpose made overflow vent would have a tube coming down below the corroplast, like the fresh water tanks does.  @TNOutback, can you see such a tube from the gray tank coming out the bottom?

 The mystery continues…. However, nüCamp has the answer to this question.
cheers

rh5555

@TNOutback, I cut the horizontal pipe first to get a bit more room, then I unscrewed the shower-pan floor support that is next to the riser from the trailer floor and twisted it to get it out of the way (it is still secured by a single screw through the plywood decking under the shower-pan.  That gave me just enough room to get my saw in.  I'd suggest laying a piece of 3/8" plywood next to the pipe to act as a saw guide because you cannot see what you're doing.  (My picture shows some 1/4" plywood which I used, but 3/8" would have been better).

I've forwarded the mod to NuCamp, who sounded interested - it would be easy to install at build time.

Denny16

In another thread here( https://tab-rv.vanillacommunity.com/discussion/13700/water-entering-gray-water-tank-under-pressure#latest),  rh5555 posted this, and it should resolve any question about an overflow outlet on the gray tank (which clears up the presence of a overflow vent raised by TNOutback’s comment above):

rh5555 said:

According to Raphael at NuCamp, there is not an intentional overflow opening at the top of the grey water tank; it should just back up into the shower pan.  Many people have attested to the fact that there is an opening, as the excess grey water drips out under the TAB, and the shower pan doesn't fill.

I can only assume that NuCamp endeavors to seal all the plumbing openings into the grey water tank but don't always succeed, or that some connections shake loose after delivery.  Hence different owners have different experiences.  

Denny16

@rh5555, installing an Hepvo valve (trap) by nüCamp at the time of build is something I have thought would be a grand idea too.  This would eliminate another hole in the TaB’s floor and be, I think) a quicker install.  The only reason not to use a Hepvo on the shower, is it eliminates the visual indication of an overfilled tank (water backing up into the shower).  But as you previously pointed out, a full tank would prevent any more water from draining from the sinks and shower, if all are installed with an Hepvo trap.  Not sure what the RIVA policy/guidelines are on this?
cheers

atlasb

rh5555, our 400 is a jul 2017 production and came with the hepvo valve in the shower.  Found it while digging around working on something else.  I Installed one in the kitchen sink and that allows more room under the counter.  Not sure about the valve preventing the water backing up in the shower with a full tank.  After a several day trip and longer showers second night found my self standing in shower water ankle deep.  Had to exit the shower and make a trip out and drain some gray water.  Lucky we were at a COE spot that allows the discharge of gray water.  We are careful now to watch the level of the tank and carry spare 5 gallon buckets with Gamma seal lids to drain gray water for dumping at the dump site. 

rh5555

That's very interesting @atlasb, I wonder why they discontinued using them.  The Hepvo valve will stop grey water backing up into the shower (from using a sink), it won't stop your shower from failing to drain once the tank is full.

Verna

Thank you, @atlasb!  I know Ed at the factory told me my 2019 T@B 400 had a Hepvo valve under the shower. He wasn’t convinced they would work well, so, I’ve been scratching my head over this discussion. 

Horigan

I have a 2019 400 and it does not have a Hepvo under the shower.  I suspect cost was a factor in switching to a P-trap...  Just saw that while spraying rodent repellant foam in the floor opening.

TNOutback

@Sharon_is_SAM I’ve only guessed there is a vent on top of the tank due to the two occasions  I’ve had gray water leaking out from under the coroplast when my gray tank was full.  I have not dropped the coroplast bottom to inspect it either.  that’s on my to-do list right after “unnecessary root canal”.

Denny16

Yes TNOutback, you probably have a loose connection on the gray tank where the drain is connected at the top, a full tank would then leak out…
cheers

Denny16

OK, after learning atlasb’s 2018 TaB400 has the Hepvo valve under the shower, and Verna adding so some 2019 models had them too, I decided to take a look under our Jan 2018 build TaB400, and low and behold, there is a Hepvo valve under the shower, and no additional hole in the floor to worry about plugging! 

Thanks everyone
cheers