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A HepvO waterless trap can "leak" in two different ways: water dripping under the sink, or odor getting past the valve into the cabin. The fixes are different, so start by working out which one you have. In almost every case, the cause is how the valve was installed or something stuck in it, not a failed valve. Everything below follows Wavin's own HepvO installation instructions for RVs. Wavin is the company that makes HepvO.
Quick diagnosis
| What you see or smell | Most likely cause | Jump to |
|---|---|---|
| Drip at one end of the valve | Slip joint: washer or seal out of place, nut cross-threaded or pipe not fully inserted | Water at a joint |
| Drip at a threaded connection | Missing PTFE tape, or the outlet cap and seal left on | Threaded joints |
| Water coming from the valve body itself | Physical damage | Valve body |
| Sewer smell at a sink with a HepvO | Valve fitted backwards, ribs up, debris in the membrane, or a venting problem | Odor getting past |
| Slow draining or water backing up | Debris, not enough slope, or a clog downstream | Slow draining |
Before anything else, dry every joint with a paper towel. Then run hot water hard and fill and drain the sink a couple of times, wiping each joint as you go. Water tends to run along the pipe, so the first damp spot you find is often below the real leak.
Water at a slip joint
Most HepvO drips come from the slip joints at each end of the valve. Wavin's instructions for a tight joint are simple, and a leak almost always means one step was missed:
- Parts in the right order. The slip nut, then the slip washer, then the rubber seal slide onto the pipe in that order.
- Pipe pushed all the way in. The pipe has to go fully into the socket. A pipe that was cut short won't reach the full socket depth.
- Clean, undamaged pipe end. Plastic pipe should have no loose shavings at the end, and metal pipe should have no burrs or sharp edges. A scratched or cracked pipe end won't seal.
- Nut square, hand-tight. Wavin says to tighten the slip nut by hand, checking it sits square to the valve body and isn't cross-threaded. Hand-tight should be enough to seal.
- No compounds. Wavin says not to use jointing compounds or chemical sealants on any HepvO connection.
The fix: put a bucket under it, back the nut off, check the seal and washer are in the right order and seated evenly, push the pipe fully home and hand-tighten the nut again, keeping it square. If the pipe end is damaged, cut it back cleanly and make sure there's still enough length to reach the full socket depth.
Check again after your next drive. Road vibration finds joints that were only just tight.
Water at a threaded connection
A HepvO can also connect by thread at either end. Two things cause leaks here:
- No PTFE tape where it's needed. If the part you're threading onto has no built-in seal (a DWV adapter, for example), Wavin says to wrap the thread with PTFE (Teflon) tape before assembly.
- Outlet cap still in place. To make a threaded connection at the outlet, you first remove the cap and rubber seal that come on the valve.
Water from the valve body
Water coming from the middle of the valve body, rather than from a joint at either end, points to physical damage. The usual culprits are knocks from items stored under the sink, or a drain snake pushed through it. Wavin warns that rodding through a HepvO can damage the parts inside. Wavin's instructions don't describe repairing the valve, so replace it. Next time you clear a clog, take the valve out first, as in our HepvO cleaning guide.
Odor getting past the valve
If the cabin smells like the gray tank even with a HepvO fitted, work through these in order:
- Is it fitted the right way round? Wavin says the valve must be installed in the direction of flow, which is marked on the body. The arrow should point away from the sink, toward the tank. Fitted backwards, it won't work as designed.
- Ribs down? If the valve is horizontal or at an angle, Wavin says the ribs must be underneath. With the ribs up, it won't drain or work as intended.
- Debris in the membrane. Hair, food or grease can hold the membrane slightly open. Take the valve out and rinse it with clean water in the direction of flow, as covered in the cleaning guide.
- Is it in the right place? Wavin's RV instructions say the HepvO goes at the fixture's outlet, or in line no more than 6 ft from it. A valve that protects a single fixture must sit upstream of any tee or branch joining another waste pipe. If another drain joins in above the valve, that drain has no protection.
- One valve per fixture. Each HepvO is meant to protect one fixture. Two fixtures can share one valve only under strict conditions, and a washing machine, dishwasher or double sink always needs its own valve.
- Check the tank vents. A HepvO replaces the trap and the separate fixture vent, but Wavin says the holding tanks still need their own vents, and every vent connection must be downstream of the valve. A blocked roof vent pushes tank gas out wherever it can. See why an RV sink smells like sewer for the full checklist.
Slow draining or water backing up
- Not enough fall. Wavin says a horizontal install needs at least 1/8" of slope per foot. The angled adapter that comes in the BV1B/UB kit is there to give you that.
- Debris in the valve. Remove and rinse it.
- A clog further down. Take the HepvO out and clear the line through the open pipe. Never push a snake through the valve.
When to replace the valve
If the valve is clean, fitted the right way round with the ribs down, every joint has been re-seated and it still drips from the body or lets odor through, it's time for a new HepvO kit. If your sink has a 1-1/4" tailpiece, get the BV1B/UA kit instead: the same valve with a 1-1/4" inlet adapter. Our install guide walks through fitting it.
FAQ
Should I tighten the slip nuts with pliers to stop a drip? No. Wavin says hand-tight should be enough. A drip almost always means a washer or seal out of place, so take the joint apart and re-seat it.
Can I put plumber's putty or pipe dope on a HepvO joint? No. Wavin says not to use jointing compounds or chemical sealants on any HepvO connection. The one exception is PTFE tape on a threaded joint with no built-in seal.
The smell started right after I installed it. What did I get wrong? Check the flow arrow first, then that the ribs are down if it's horizontal. Those two cause most new-install odor problems.
Can blowing out the lines for winter damage it? Keep blow-out air at or below 80–100 psi, the limit in Wavin's RV instructions.
Does a drain cleaner damage the seal? Standard caustic drain cleaners are fine, and so are acid cleaners up to 10%. For anything stronger, remove the valve first. See the HepvO cleaning guide.