Just the thought of using a run-down worn out grey and black combo sewage tank makes me shiver. More than shiver, these dinosaurs have a little if any capacity to protect trailer occupants and stay sanitized.
Imagine the lack of efficiency of all the fittings, decomposed glue, and worn out plastic. Therefore, there is no efficiency with any connections. For all to see, this is a health hazard and a must to rehab the rotted molding flooring as well as the frame which the tank sits on and probably leaks continuously.