[jcurtis934]

Since you are talking both grey tanks...are you leaving the valves open and allowing the sewer gases into your tanks...hence into your plumbing? The shower, with its rubber one way flap gizmo really doesn't seal all that well and tank vapors will still invade the rv unless stoppered with a rubber plug. You don't say what model or year montana, so you may also have one with a air admitance valve under the sink in spite of also having a roof vent for the kitchen sink. If so, cheap vents almost always stick partially open and allow gases into rv. This can be capped off in most cases. Chemicals...since the drain pipes are just like home, most things won't hurt them. Vinegar is a extremely weak acid and baking soda a weak alkaline whick is not harmful...but I think you would have to dump in a lot to do any good. I think I would add an enzyme cleaner and allow it to work first. John