[Coolbreeze]

Couple of things:

1) I agree with how your being coached. Dump full, clear pipe, change paper, etc.
2) I also have a Mako and the pipe is straight and I can see into the tank. Are you sure your's isn't straight.?I can also tell that since the black tank is the middle tank, e.g , fresh water is furthest back, then kitchen, then black then bathroom.
3) You must have an enormous clog and I could imagine a screw put through the two pipes to hold them together. I would be a dumb move but lets just say I could imagine it.
4) Always flush with a lot of water then your tank will fill up quicker. With four in my camper I always run out of gray tank capacity before black so if you dump extra water down the black who cares.
5) I always flush the black tank twice when I'm at the campground and often once when I get home.
6) Add a cup of Calgon Water Softener to the black tank to help things from getting stuck.