Wow, sounds like you've got some things to iron out. First, welcome to the MOC. This is your best source for information regarding your Montana. It sounds like you're going to have to go through your breakers one at a time and figure out what does what, and then mark them accordingly. Schematics are very difficult to come by on these rigs, as I understand, for various reasons. The sensors on the black tank tend to get dirty quickly and become useless. It sounds like your back-flow valve is clogged or malfunctioning if your flush isn't getting to the tank, assuming you're using the black tank flush. As far as the manual goes, yeah, it's very generic but you should have paperwork regarding all the different systems in your camper. They may help. Others will chime in with their expertise here, of which there is plenty. Good luck.
2010 Montana 3455SA, Mor/Ryde pin, wet bolts, TST 507, Progressive HW50C, GY G614
2019 Silverado D/A 3500HD LTZ DRW CC