I followed Dave's lead and contacted Thor for the plumbing and electric schematics. My bathroom sink drains into the Black Tank.
Another way to check where something is draining is to dump all of the tanks. Then if you want to know where the shower drains, pour a 1/2 gallon of RV antifreeze down the shower. Put a clear plastic fitting in line with the sewer hose and dump one tank at a time. When you see pink, that is where the shower is plumbed to.
Fred
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