Shower won't drain unless gray valve is pulled

[Jenkins6]

Hello All.  My husband and I are new to the RV world, although my parents and grandparents have had them for years!  We recently purchased a 2008 Frontier Explorer and have loved it so far.  The only problem we've found with it is that the shower will not drain unless you go outside to pull the gray valve.

The previous owners had purchased an extended warranty on the RV and we had it transferred to us, so we took it in for repairs but the shop told us that they can't see anything wrong with the shower and that all the vent lines are clear so we should just leave the gray valve open and move on with life - but I've been raised that you don't let your tank empty at your site - that it's bad form.  Maybe we're being too uptight about that, but either way, it doesn't seem like this is a normal problem to have!

Has anyone else had this problem and if so, how did you fix it?  I appreciate your feedback!

 

[Ned]

Does it not drain at all or just very slowly?  I would suspect the gray water holding tank vent pipe is plugged.  You can check it from the roof to see if it's open or not.

As for leaving the gray tank drain open, most of us do just that when we're parked for a while and hooked up to a sewer connection.  But it's not the solution to your problem but is a temporary work around.

 

[Jenkins6]

It doesn't drain at all.  We took it to the shop and they've said all the vent lines are clear and there are no clogs in the drain lines either.

 

[Rene T]

This may sound way out but were the previous owners the actual original owners? Did the previous owners have the same issue?  Is it possible that someone for whatever reason, remove that tank and just connected the pipes together. That may sound dumb, but what else could it be?

 

[carson]

I would call this a true enigma. There must be 2 or 3 ways to explain that. Where is JFD.

 

[donn]

Either that or your gray tank is full!.  Open the gray tank valve and let the water drain.  Once it is empty, take a flash light and look up there to see if there is a piece of construction debris plugging the drain.

 

[Rene T]

After trying what Donn said, How about trying this: After the tank is empty, close the drain valve. Then using a 5 gallon bucket, see how many it takes to get to the point where you see the water in the shower. If it only takes let's say one, You may not have a tank. Boy that sounds so stupid. I can't believe I'm thinking that way!!!!

 

[kenz]

First off, I'd have a problem with  ..."just leave the gray valve open and move on with life"... as a viable solution. My personal opinion is find another RV tech. First off the valve should be opened only when hooked to a sewer connection. Not a good idea to just drain on the ground, not sanitary and the neighbors probably wouldn't appreciate it much. To break it down, I would think that it should have a gray tank. Even in the possibility of the previous owner removing it, the RV tech should have noticed this and told you there wasn't a holding tank. I'm gonna assume that the tank is still there.

Now with that being said, if it only drains when the valve is open, that means the vent doesn't work. On all the ones I've seen the black and gray vents are usually connected together for one vent line thru the ceiling. On my last couple trailers the vent tube went straight to the black tank and branched off to the gray tank. So anything run down the vent from the ceiling whether a rod or water stream, will go straight to the black tank and not around the corner into the gray tank. Couple ways to find out for sure. Find and cut the vent to the gray tank where it hooks to the main vent. Run a rod or look with a flashlight to clear or see what may be the problem. A rubber boot/hose connector can be used to reconnect the line. The other idea, which will incur a fee, but will tell for sure is to contact a plumber/sewer guy. The more established ones will have a snake with a camera on it that they can run up the piping and that will show what's going on guaranteed.

Good luck and let us know what you find.

 

[judway]

The drainage of our shower depends on the leveling of the MH from front to back. If the front is higher the drainage is poor. If the front is lower the drainage is good. Our shower is on the opposite side from the gray water tank.

 

[Icemaker]

No body that I've seen yet asked if the sinks drain as they should...if they do than the issue is the shower drain... which would suggest a hair or soap clog ..if this is indeed the issue...on the other hand if they all drain poorly it's back to the vent and cutting the vent is a fool proof way to check that out..and easy to reconnect too.

George

 

[Rene T]

George, they said that it did drain only when they opened the tank drain valve outside. It doesn't sound to me like a clogged shower pipe.

 

[Wavery]

You need to get a plumbing schematic and see where your shower is vented and where the shower trap is located. Also check for one-way check valves in the drain lines. If the drains are sharing a common vent, there could be a check valve that prevents water from a sink traveling down to the tub.

It makes no sense that the holding tank vent would cause this issue. That would effect the sink drains also. Either the sinks would drain into the tub or the air would escape through a different drain.

 

[Gary RV_Wizard]

It makes no sense that the holding tank vent would cause this issue. That would effect the sink drains also. Either the sinks would drain into the tub or the air would escape through a different drain.

That seems right, at least in theory, but the shower drain is the lowest point above the gray tank, so is the first place you see a problem. It's also usually the largest volume of water. I know in my own coach the shower drain slows down while the sink drains continue to work, giving me warning of an impending  problem. I think the extra length of pipe plus the smaller water volume sometimes lets the sink appear to drain when it is just filling the available pipe. If the lines are slowly draining into the tank, then the pipe empties before more water is added and we perceive that the sinks work ok when in fact they also have a problem. One way to test this is to fill the kitchen sink with water and then pull the plug to see how well the drain handles a sudden large volume. You may find it slow, or you may find the sink water backing up into the shower.

I would start with drain cleaner in the shower, perhaps a couple applications. Let it work overnight.  Also clean out the hair in the throat of the drain. Get the shower drain line running at full capacity and see if the problem goes away.  For a partially clogged drain, I prefer a paste type drain cleaner that clings to the gunk. Pure liquid types tend to run on through without making much contact with the clog mass.

 

[catblaster]

  It's my turn to take a stab at this......It acts like its airlocked which is usually caused by "double trapping". you have the P-trap under the shower and before the pipe gets to a vent or the tank it gets a sag in it equal to or grater than the diameter of the pipe. A shower cannot get enough head pressure to overcome this like a sink or tub can.
  Another problem is they could have piped it to the bottom of the tank but even then it should drain a little. Air should never escape through a drain as mentioned before, that is the purpose of a water seal, air should only move in or out of a vent. Air admittance valves are exactly what they are named "admittance" they should not allow air to escape which is what is needed if the drain is installed so as to create a double trap
  Nothing can take the place of a taking a good look underneath or running a camera thru the pipe. Be careful with the drain cleaner, once it is put in the system you may find that no one wants to put their camera thru that. It also can  make some nasty burns for the poor worker that cuts out a badly installed system.

 

[jim and di]

You might try to use a vacuum cleaner with a hose attachment. I have pulled out many a clog with the shop vac. do not try this if you have put in the drain cleaner. If the pipe to the tank is clear you will here a good volume of air rushing through the pipe.
Jim

 

[Wavery]

You might try to use a vacuum cleaner with a hose attachment. I have pulled out many a clog with the shop vac. do not try this if you have put in the drain cleaner. If the pipe to the tank is clear you will here a good volume of air rushing through the pipe.
Jim

Now that's a good idea......... conversely, you also may try compressed air through the line.

One of the reasons that you need a plumbing schematic is to find things like double traps.

Have you tried filling the tub with water, then letting it drain with the grey valve closed?

 

[Lou Schneider]

I had a Sierra 5th wheel where the tub drain shared a common pipe with the tank's vent line.  This is common practice in stick and brick houses, where the roof vent is an extension of the drain line and serves to break the suction inside the drain.  RVs usually have a dedicated tank vent that is run through the roof and mechanical vacuum breakers at the top of each drain line.

Sharing the tank's vent stack with the tub drain produced symptoms similar to what  Jenkins6 reported - it worked fine whenever the RV was connected to a sewer, but with the grey valve closed, the tank would pressurize any time the line filled with water and the tub would stop draining until the water flow into the shared vent/drain pipe was interrupted and allowed the tank pressure to vent to the roof.

All of the other drains worked fine, as long as the tub drain wasn't in use the tank vent operated normally.

The tub drain worked well enough during Navy showers, where you run the water in short spurts then turn it off while soaping up.  But water tended to back up during an extended shower and draining a filled tub into a closed tank required manually plugging and then re-opening the drain several times to get it to drain completely.

 

[Lowell]

I wonder if the builders assumed that one would only use the shower when connected to a sewer, not dry campings where water is in short supply. Not a good assumption. 

I think Lou's comment is a good possibility.

 

[Jenkins6]

Thank you for all the suggestions!  This is a place I'll be coming back regularly!!

The sinks drain just fine, no problems there ever.

We do have a grey tank - we checked that ourselves. 

There's no clog in the drain, because when the grey valve is opened it drains perfectly fine - very fast even.

I'll try some of the other suggestions and see what we can come up with.  Basically my husband called the repair shop back today (I was the one who spoke to them yesterday) and they didn't give him the runaround they gave me - they just said they spent 6 hours on it and can't figure it out!!

 

[Wavery]

I had a Sierra 5th wheel where the tub drain shared a common pipe with the tank's vent line.  This is common practice in stick and brick houses, where the roof vent is an extension of the drain line and serves to break the suction inside the drain.  RVs usually have a dedicated tank vent that is run through the roof and mechanical vacuum breakers at the top of each drain line.

Sharing the tank's vent stack with the tub drain produced symptoms similar to what  Jenkins6 reported - it worked fine whenever the RV was connected to a sewer, but with the grey valve closed, the tank would pressurize any time the line filled with water and the tub would stop draining until the water flow into the shared vent/drain pipe was interrupted and allowed the tank pressure to vent to the roof.

All of the other drains worked fine, as long as the tub drain wasn't in use the tank vent operated normally.

The tub drain worked well enough during Navy showers, where you run the water in short spurts then turn it off while soaping up.  But water tended to back up during an extended shower and draining a filled tub into a closed tank required manually plugging and then re-opening the drain several times to get it to drain completely.

That's why I suggested filling the tub and letting it drain. If there is enough water weight, the pressure in the tank would have to be released at some point. The water would "Glug" down in spurts.

I still think the answer is in the plumbing schematics......... My bet is that there is a trap (or double trap) where there shouldn't be.