[DQDick]

If that doesn't solve the problem, the next thing to try is check the Hepvo valve. Many, if not all, Montanas have at least one under the shower in the drain line usually found along the drain line on the ceiling of the basement either behind the wall or before the wall. On our rigs it's been one place or the other but we have had it either place. What it is (look it up on Amazon to see what it looks like) is a substitute for a P trap where they didn't want to put a P trap. The issue is it has a membrane inside that keeps sewer smell from coming back into the rig, but if you don't take out the drain cover in the shower and replace it with a screen that will catch the hair etc the hair will clog up the Hepvo valve then someone sticks something down the drain thinking they'll poke a hole in the clog and instead they poke a hole in the membrane. You can remove the Hepvo valve and clean the membrane with a soft brush, but I'm lazy and prefer to catch the hair before it gets there.