Upgrading the RV Drain System with a HepvO Valve

A little while ago I released a blog post explaining the operation of a plumbing part called an Anti-Siphon Trap Vent Device (ASTVD) and how a failure of it could lead to waste tank odors making their way into the RV.

At that time, I indicated plans to install what’s called a HepvO valve as a replacement to the traditional P-Trap.

My friend Doug from DrainMaster.com had highly recommended the HepvO valve as an upgrade. So while RVing our way north this spring I stopped into his place in Hollister, CA and picked one up.

HepvO drain valve

What is a HepvO valve

The HepvO valve is a plastic tube with a one-way valve inside. The valve is made from a special flexible material allowing drain water to pass through but closing up airtight once it does. The ends have threaded couplers with rubber seals so it can be easily connected to existing plumbing pipes and quickly removed if necessary. The HepvO valve comes in 1 ½ and 1 ¼ inch diameters.

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Why Is the HepvO Valve an Upgrade?

There are several reasons the HepvO is better than the traditional P-Trap used in most RV drains.

  • Unlike a P-Trap the HepvO requires no water to seal off nasty waste tank odors
  • Since the valve is waterless there is zero chance of freeze damage
  • Water can evaporate from a P-Trap letting tank odors in the rig
  • Water can be siphoned out of a P-trap when dumping he waste tanks
  • Water can be lost from the P-trap during travel
  • No secondary venting is required so the ASTVD can be removed
  • The HepvO system takes less space freeing up valuable RV storage

Installing a HepvO Valve in the RV Drain Plumbing

The HepvO gets installed in place of the P-Trap mounted either horizontally or vertically. Depending on the existing RV plumbing some extra adapters may be required but is easily done by most DIY RVers.

HepvO installed

I installed the HepvO for my Keystone Cougar fifth wheels kitchen sink drain vertically. Due to the way the plumbing was routed and the tight quarters, I decided to place the HepvO vertically inline near the floor.

It was a bit more difficult of an install because of this. The 1 ½” drain pipe in that location had a heavier wall so would not fit the HepvO without a pair of pipe size adapters. It turns out two sizes of 1 ½” plumbing pipe was used in my Cougar with differing wall thickness.

Installing the HepvO Valve in RV Kitchen Drain Video

It took a bit of extra work and pieces to get the HepvO installed the way I wanted it but I’m really happy with the end result. I have more usable space in my under the sink cabinet and an end to smelly sink odors.

* HepVo Update Video 9 Months Later*

See More Love Your RV! Mods and Upgrades

Installing a HepvO drain in place of a P-trap to upgrade the RV drain plumbing by the Love Your RV blog - http://www.loveyourrv.com/ #RV #DIY #RVupgrades

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  • Troy D.

    When I first came across this trap, I thought it would be a great solution for a tiny house as there is limited depth to the floor and no basement. It seemed like an ideal way to avoid a traditional P-trap, and the problems associated with freezing, heat tape, etc. The fact that they take up less depth also meant I could add extra Insulation. I was sold, bought two.

    Well, everything was working fine until it hit about 30 below zero here in Alaska. I can tell you that this bladder material doesn’t fair very well in the cold temperatures, and I believe residual water also causes the membrane to stick together.

    I vacuumed all the still water out of my bathtub, and poured boiling water down the trap and nothing. I even ran repeated applications of the boiling water, sucking out the excess water each time. Nothing! Frozen.

    So, I just wanted to let other people know that while this seem like a great idea on the surface, the trap has problems in the cold. I will now remove this, and go back to a traditional P-trap with heat tape. Unfortunately I won’t be able to do anything until the temperatures get a whole lot warmer, so this caused a real big headache for me.

    I may have to tent the underside of my tiny house and pump in some heat to work. Current temperatures are about 20 below zero. So, the last thing I wanted to do was deal with a P-trap in the cold, which is why I bought this thing to begin with. So, again, very disappointed, and wanted to warn others that this is not something that I would recommend for a cold climate.

    • Thanks for the comment Troy, good to know for any extreme cold weather RVers or tiny house owners. One thing about RVs though is the p-traps are generally inside the living space so I don’t envision a problem since they will be kept above well freezing and when in storage the pipes have been drained. Did you contact the HepVo company? If so what was their response?

      • Troy D.

        Yes, the company did respond. Essentially they have done very little scientific testing, other than putting the valve in a freezer. My guess is that it takes a certain amount of water weight to actually open the bladder, so the valve is really not waterless as claimed. No doubt it would work better in a vertical application then horizontal. I suspect if the bladder material was made thin enough so that resistance was minimal, the bladder material itself would become rigid in the cold and not function.

        So, while the concept of this is good, the practical reality is it’s really not a cold weather trap and cannot be trusted. I will be going back to a traditional P-trap, and a short length of 3 watt heat tape. 9 watts (3 feet) of tape would probably be adequate to keep the trap from freezing.

  • D curtis

    Ray, just a follow up on this, have you any problems with this system? My concern is that, over time, the rubber valve may degrade and fail, so, I wanted to do a follow up question to see how it’s doing.

    • I haven’t taken it apart to look yet, but it still drains well. Also, we haven’t had any smells in the RV from the sink, even when I had it in storage a few months, so I’m pleased.

      • D curtis

        Thank you so much for the reply, Ray.. very much appreciated.

  • David Guenthner

    Did you install these in your other gray tank inlets in the bathroom?

    • No, I’ve installed only one in the kitchen drain. So far it seems to be working out well so will likely add one to the bathroom drain next.

  • Kevin Martin


    Your pipe sizing problems have nothing to do with RV’s. Almost every kitchen
    sink will have both pipe sizes under them.

    The “larger” pipe (DWV) sizes are named based on approximate inside
    diameter, and 1 1/2″ pipe is almost 2″ outside diameter.

    The “smaller” pipe between the sink baskets and the trap (and
    sometimes including the trap itself) use a different sizing system, where the
    nominal size is exactly the outside diameter. These are often encountered as
    thin-walled (possibly plated) brass pieces directly below the sink drain
    baskets. The point where they transition to DWV pipe depends on the

    These pipes are commonly connected using slip-fit joints.

    By the way, “DWV” means “Drain-Waste-Vent”. I cannot,
    however, for the life of me figure out what that other pipe sizing system is
    actually called.

    • Thanks for the info Kevin. I tried 2 hardware stores and a trade plumbing supply place and the only thin walled drain pipe they had was the short straight piece that fits right under the sink. Couldn’t find any elbows or raw pipe in that size. Would have made it a lot easier.
      I’ve since learned about pipe schedules. The thinner stuff is schedule 20 and the thicker stuff is schedule 40 according to one YouTube commenter.

      • Kevin Martin

        The different “schedules” of pipe all share the same outside diameter for a given nominal size so they can all share the same fittings.

        Indeed, about all you can find for this pipe size system is the drain tailpieces and the connections required to run a double sink to a single trap.

  • Brian G

    Ray, I love your videos and mods. They have been really helpful with my rig but I have to say this seems like one of those that falls in the way to much work for little reward category, lol! 🙂

    • haha, ya. Luckily it’s fun for me. 🙂