[JRTJH]

The tub, sink and toilet in our S&B all connect to the same sewer dump in both out bathrooms, all within 4 or 5 feet of each other for each bath. Conceivably, if the sewer line was plugged downstream from either bath and someone flushed the toilet, it would back up into the tub.

I've seen a number of RV's with the outdoor kitchen sink dumping into the black tank with only a HEPVO trap (nothing more than a balloon inside a PVC pipe). On most RV's with a second "half bath" there is only one tank for the toilet and the sink. Routinely, on larger "two bath models" there's three tanks (2 gray and 1 black) for the front components (kitchen, front bath and toilet) and one tank for both the toilet and sink in the back of the RV.