Overflowing Shower/Lavatory Drain - I've tried everything

[djg_78g]

Hello all,

I bought a used 06 Montana Mountaineer 329RLS recently. The lavatory (sink/shower) seems to not want to drain properly. When I run either the sink or the shower, water backs up into the tub basin and doesn't drain at all. The grey tank is empty. I've tried the baking soda and vinegar thing, that didn't work. I removed the P trap under the tub, it is clear of obstructions. I snaked the drain after the trap all the way to the tank. (my entire 15' drain snake). I thought it might be the inline vent, but there doesn't seem to be one on the bathroom plumbing like there is in the kitchen. i cleaned some mud dauber nests out of the grey tank roof vent, that did't seem to help either. What could I be missing? Thanks in advance for any advice.

[Eastham]

Sounds like the tank is full is there a possibility that the handle on the slide valve is not functioning properly. Does it eventually drain out of the tub after it sets for a while.maybe there is a different slide valve for that gray tank.just a crazy idea but I would run the snake up the drain from the outside and have someone listen in Side and see if you hear any noise in the tank or if the snake stops at the slide valve. Probably a crazy way to do it but you never know.

[djg_78g]

Thanks for the suggestions. I'll look into that. It doesn't seem to drain at all. However, if i run some water into the tank from the kitchen sink it dumps out so i dont think its the valve its self.

[tech740]

Sounds like you have 2 gray tanks. One for the galley and one for the bathroom sink and shower. You probably have another handle you have not located yet. Get low and look for another handle under the camper someplace. Usually placed in a hard to reach are at the edge of a slide.

[nied]

2 Grey tanks? A second valve?

[djg_78g]

There is in fact a second grey tank. I feel like a dummy but now everything works as it should.

[Eastham]

Dont feel bad.it happens all the time.
Good luck with your new rv.now that the tank is empty get on the road and fill it up again.