NOT REALLY SOLVED!! R Pod 171 Shower Wont Drain!

Welcome to the forum and you are on the right track.  I am not sure of the floor plan of your 171.  I have a 2019 179 and the sink drain line is connected into the shower drain line on the passenger side of the trailer.  Then the drain is piped to the other side of the trailer through the flooring.  On the driver's side of the trailer the kitchen sink is connected to the one  "common" drain line to the gray water tank, which has no venting.  All drains have a P-traps to hold back the sewer gasses.  Depending on how your drain lines are connected (you didn't mention if the bathroom sink has a problem draining also) you may just have a partial obstruction in the problem drain line. The obstruction could be as simple as being in the shower's p-trap.  Be careful when trying to dislodge any obstruction because the drain line joints will not tolerate a lot of pressure, it's all plastic piping. This is just my understaning and I hope it helps you.

Hey guys thanks for the input!

Edited by zachthecamper - 25 Aug 2025 at 10:46am

Glad you found it and were able to get it fixed.  Thanks for sharing with everyone.  That's something you don't come across very often. Now enjoy your shower!!

Update — I spoke too soon.

Removing the vent did allow the system to drain, but once I installed the new vent, the exact same problem came back. I had the vent off for a few days while waiting on the part during a trip, so I thought the issue was solved. When the new vent went on and the problem returned, I never updated the thread. Hopefully no one has already gone down a rabbit hole because of that—sorry if so.

Here’s the actual issue, which I currently have band-aided:

The shower isn’t draining because R-Pod (or a previous owner) installed a waterless P-trap between the roof vent and the gray tank on the shower branch. The passenger-side plumbing is routed like this:

Shower drain + shower sink → roof vent → waterless P-trap → gray tank

Because of this layout, the kitchen plumbing on the driver side cannot breathe through the roof vent. The one-way waterless P-trap blocks positive air from traveling up to the vent. When water runs through the kitchen sink, the system becomes pressurized, which prevents the shower from draining.

The only ways to break the vacuum are:

1. Removing the mushroom vent under the kitchen sink, or

2. Opening the exterior gray tank dump valve

Neither is practical. Option one lets gray smells into the camper, and option two requires being hooked up to a drain—obviously not ideal when boondocking.

My current temporary fix:
I removed the internals of the waterless P-trap so it’s now just a pass-through pipe. Everything drains correctly this way, but on hot Texas days, gray tank gas comes up through the shower drain since the trap is no longer functional.

What I believe is the correct fix:
Relocate the waterless P-trap closer to the shower, before the roof vent. The plumbing order should be:

Shower sink → shower drain → P-trap → roof vent → gray tank

This would allow the gray tank to vent freely through the roof and give the kitchen plumbing a proper path to release positive pressure when draining.

The key issue is that the mushroom vent’s job is to allow air in, not release positive pressure (for obvious odor reasons). With the current setup, the kitchen side can only pull air in—it can’t push air out—resulting in the vacuum lock.

I also confirmed the roof vent itself is clear. I got on the roof, flushed it with a hose, and could feel air moving while running water. The vent is not obstructed.

Typically, when you have two separate plumbing trees (driver and passenger sides), manufacturers use two roof vents. R-Pod chose to run both sides and the black tank into a single roof vent. Simpler, yes—but not effective in this configuration.

So my big question is:
Is this the OEM setup and just a major engineering miss, or did a previous owner (or their mechanic) decide to “improve” things?

If anyone with an R-Pod 171 could lift the small square plywood panel behind the bathroom and check how their wet bath P-trap is routed, that would be incredibly helpful.

I’m open to the idea that I may be missing something, but based on everything I’ve researched, tested, and observed, it really seems like the waterless P-trap is simply installed in the wrong location for proper venting.