OK, front Sani-Flush works, how can I tell? You can feel the flow through the hose and see water coming out of clear 45 degree connection, I too at first camp out thought rear sani-flush was working until I got home and hook up and have time just to let the systems flush, I found rear hose hard and no flow, traced to under rear bathroom sink and inlet hose from connection was hard as a rock with outlet from h check valve soft...turned off water and depressured outside and turned h check valve. Swapped inlet and outlet of h shaped check valve/siphon breaker and voila we have sani-flush to rear tank, just think of an h the inlet goes to the bottom left of the h and the outlet comes from the bottom of the upside n right side of h. PM me if not sure. Will try paint program and draw up something.....
2014 Voltage 3950
2013 F-350 DRW Lariat