Weird Plunbing Issue

[Joel Ashley]

Sure n' begorra!

[Bill Sprague]

I'm not completely sure of this, but it might be your vent.  

My understanding is that in a house, all the drains have vents that go through the roof.  Their purpose is to allow free flow of air into the drains behind the draining water so that it drains quickly.

Our motorhomes don't have those.  Instead we have a type of vent under the sink that is a one way check valve for air.  My motorhome has two.  They are under the bathroom sinks.  The kitchen sink does not have one that I can see.  It might be hidden.

The check valve vents can have two failure modes:  stuck open or stuck closed.  Open can cause hard to find odors and closed can cause drains to be slow.  

I'm not sure, but I think they can be unscrewed and replaced.  I don't think they are glued on.  

If your shower shares the vent with the sink, and the vent is stuck, it might be the cause of your shower drain problem.  

Dick's suggestion that his is worse after it has been stored for awhile suggests that his might be only a little sticky and gets better with exercise.  

Good luck.  If these motorhomes were easy to figure out, everyone would have one!

[John Hennessey]

We were having the same slow running shower drain which was probably due to a hair clog so I heated up 4 cups of water to around 185 degrees and poured it down the drain.  Then I took pantene hair conditioner and squired some down the drain and followed up with another 4 cups of hot water and it cured the issue.

[Joel Ashley]

Hmmmm...
That's the last time I use Pantene on my hair.