New ta me TT. Has two water supply bibs. Figured out bottom is for supply water. Think tha top one is a black tank flush but cannot tell for sure. It goes to what looks like some type of regulator the...
If your black tank is empty hook it up to the one you think is the flush, crack open the black and see if water comes out. If it's been used but still empty then maybe a 5 gal bucket under the sewer drain.