Black tank flushing


New Member
I have a Columbus Palomino FB 383. It has 2 black tank knife valve pull handles. 1 upper toilet(main) and 1 downstairs. When I try to empty 1 at a time pulling the upstairs toilet drain nothing flows. If I pull the downstairs handle then the up stairs will drain. Does the upper empty through the downstairs tank??? I cannot find a plumbing schematic and online I cannot find either???