I will try and get a picture of the inside drain pipes this weekend :) there are the black drain pipes and there is a handle that you pull out to drain the pipe but there also is at the back of the camper a little knob that you turn and the grey water comes out. I also am confused about the handle and the knob outside. when we had our toy hauler you had 2 handles outside underneath 1 for black that you pulled first and then the grey water handle that the grey water would help rinse the septic hose of residue and then wash out. Really Easy Peasy stuff Never had a TC and how it works and why. the back up could very well be that the grey is full but the gages tell us its empty. Hopefully well get over to it this weekend and figure it out. Its fall time here in the NW so we have all fall and winter to tear apart and figure out.