poopy--poopy OH MY

[Carl n Susan]

It sure sounds like your black tank check valve has bit the dust. It is intended to prevent a back flow situation. There have been lots of discussions about these beauties. Do a "search" on "black tank check valve" and there will be a lot of postings. Here is one with pictures:

http://www.montanaowners.com/forums/...lve,black,tank

I believe the check valve is installed behind the shower in a 2955 but may be in the bathroom sink cabinet. Look in the pantry for an access panel.