On my bath and a half there is one black tank One gray tank and one "Wash" tank. (Wash is gray water without the kitchen sink) This is important to know because the rules for dumping are different.
Back: MUST be dumped into a proper sewer system (NO exceptions never dump in a storm drain or on the ground, ONLY into a proper Dumps station or hook up or other sanitary sewer system)
Gray: Most places ... same as black, but in a few places you can ground dump.
Wash: Many (not all) areas you can ground dump
But there is only one black tank. IN my RV the black tank and the "Front" Half bath are "Amidships" about half way from front to rear. in front of the rear axle, It has a "Gravity" type toilet (Standard RV type). The Full bath is in the very rear and has a macerator toilet that "pumps" the waste to the back tank .
The only complaint I have is about the front toilet, it has a "Round" seat, In prefer an "oval" shaped one.