Need Advice Repairing Leaking Drain Pipe

[mdmarmd]

I have a 2017 Montana Montana 3720RL. When I was closing it up for storage last fall, I noticed a damp spot on the carpet on the slide out tray on the front compartment. I traced the source to a threaded ABS drain fitting in the overhead of the forward compartment. The threaded area has some type of joint compound on it and I could feel it was moist.

This spring I need to fix this so I just wanted any advice on the best way to approach this. I just don't want to damage anything, especially the inaccessible part extending up into the floor. I believe this is a grey water drain that receives water from the shower, sink and washing machine. I am pretty sure the balckwater drain from the toilet is on the other side of the forward compartment.

Is it OK to just try and grasp the top and lower collar and twist to tighten the joint? Or do I need to unscrew the fitting and apply new joint compound to the threads. I am not where the RV is currently, so I don't know if this would require cutting the lower pipe first and then finding some kind of adaptor to reconnect it.

I think the pipe is a 4 inch pipe, but I'm not certain. Maybe it can be determined by the limited pictures I took.

Thanks for any advice,

Doug

[MandK]

It looks like your 3” toilet drain. The threaded coupling you see with the pipe dope on it is a 3” male pipe thread x 3” female slip abs coupling. The abs compatible pipe dope remains moist. The best way to tell if there is water laying on those threads is to touch a blue paper shop towel like blue Scott shop towels to the joint. If water is there it will be clearly noticeable on the shop towel. The moist pipe dope won’t make a wet spot on the towel.
The shoulder that you see going up through the floor is the bottom of the toilet floor flange that screws onto the coupling described above. There is a possibility that this threaded connection could be loose but a more likely scenario would be that the rubber flange seal on the bottom of the toilet is leaking and water is finding it’s way under the flange and down through the hole in the floor. This could be because the gasket is shot or the floor flange is cracked. Look to see if the floor opening is showing signs of being wet or past leaking.
The fix will be to remove the toilet, remove the screws that hold the floor flange to the floor and remove it, clean up the old pipe dope, apply new pipe dope and reinstall the floor flange. Tighten it until it is as snug as it will reasonably go and still keep the flange bolts that hold the toilet at the 3 and 9 o’clock positions. Screw it back down to the floor and Install a new flange gasket on the bottom of the toilet and reset it.
I had this same issue a while back and replaced the flange gasket. When I did, I saw that they overtightened the flange bolts when they installed the toilet and cracked the flange. In my case the crack is such that the flange is not cracked though to the inside and the new gasket solved my problem. I ordered another gasket kit and a new floor flange for my parts bin in case I have trouble with it again but so far it has been no problem. We are living in our coach for the winter and have the spare parts right here so let me know if you need part numbers for the gasket kit and flange if you need them. Good luck.

[newowneroldmontana]

Thank you, MandK. I have a different year and model, but I think you've given me the fix to my same-ish problem.

[mdmarmd]

Your explanation is very helpful and clarifies some confusion I was having.

I had tried to determine the source of the pipe by tapping on it while my wife tried to localize the sound on the bathroom floor. She identified a point on the floor that made me think it was a drain connecting the washing machine outflow and the shower and sink drains. At the time, it seemed it was to the left of the toilet, about as far over as the middle of the doorway. I knew the washing machine and shower drains were connected because the flapper valve in the shower drain was pushed backward once by the outflow pressure from the washing machine.

Of course I didn't know what the toilet floor flange looked like at the time.

After reading your explanation, I lined up a picture of the RV with one of the floor diagram and its pretty clear that the toilet really does line up with the position of the leaking pipe.

The camp doesn't open up until around mid April depending on the snow pack. So, I won't be addressing this until then. If I have any questions then, may I contact you if needed?

Thanks.

Doug

[mdmarmd]

MandK,

I am pretty sure water is leaking from this fitting as the position of the moist spot on the slide out tray carpet is right below the drain. I recall feeling moisture around the threads. I guess it could be coming through the hole in the floor, but then it would have to track down the outside of that fitting and then into where the thread are. If I can isolate the leaking just to the threads, does it make sense to just try and tighten the pipe and see if the leaking stops? Or is it safer to actually remove the toilet to be certain moisture is not getting into the flooring?

I am reminded that I might have another reason to remove the toilet. I wanted to ask you whether you have a Dometic or Thedford toilet?

Last summer the water in my toilet was not holding in the bowl. It would just leak through the toilet ball seal. I kept trying to pull out the seal to replace it as I had done previously and couldn't pull it out. It finally dawned on me that when I replaced it before it was in the Holiday Rambler Presidential that I had before. So, doing some research I realized that the previous toilet must have been a Dometic and the current one is a Thetford. How much easier it is to change this seal on the Dometic. The Thedford requires removing the whole toilet just to change this seal. So, I was going to order the replacement parts last summer, but after pouring CLR and vineger into the bowel multiple times, it seemed to disolve the crusting on the surface of the seal enough to stop the leaking. So, if the ball seal is leaking again, I guess it will give me another reason to open things up anyway.

[MandK]

I have a Dometic. The ball seal replacement is very simple. I am not familiar with the Thetfords.
To “tighten the pipe” you would have to cut the pipe and then mend it after. To tighten the flange, you would have to get a quarter turn on it to align the flange bolts. Your particular installation may determine your best path forward.

[Daryles]

Mdmarmd,
For the toilet bowel not holding water.
"Crusty stuff" builds up on the bottom surface of the black rubber seal that the white flush ball seals against.
With Dometic Toilets you can just pull the seal out and clean it or replace it.
With Thetford Toilets you have to remove the toilet and split it in half to replace the seal. It can be done NOT removing the toilet. Not hard just awkward. Look for YouTube videos.
OR
Take an old toothbrush.
Heat the handle and bend the head 90⁰ to make a hook.
Hold the flush valve open and scrub the bottom side of the black rubber seal. Use vinegar, or CLR to break loose any lime scale build up.
Use a generous blob of plumbers grease (silicon) on the BOTTOM of the seal. Use your finger.
Cycle the foot pedal many times to be sure the silicon coats the seal and re coat the bottom of the seal if necessary.
Test.
IF you are removing the toilet anyway to replace the floor seal, replace this ball valve seal while you have the toilet out. Again make sure you lubricate the seal with a generous blob of silicon.

[mdmarmd]

Thanks for the additional input.

[twindman]

I bought toilet seal for a Dometic a few years ago. I think it was only $10 or $15 for 3 gaskets. I thought i was getting one, but the package had 3!!! Very easy to pull out and replace - just follow the directions.
Oh, also, I use plumbers gasket grease once or twice a summer and clean it up each time.