Best way to deal with the black tank is to (literally) flush the crap out of it after every outing.
This can be a PITA at campgrounds where you have to wait in line for your turn, then you dump and feel rushed to get out.
I bought a flojet macerator (AKA: poop cannon) and now can flush as much as I want (ohh that one was was a bad pun) at home in the driveway at my leisure.
I just run the hose into a toilet and give 'er!
A better solution would be to have a direct line into the house stack, but that's beyond my reach at the moment.
My trailer is also further aided by the built in black tank flush system.
Just keep spraying and pumping until clear....no smells afterwards.