Hey Crent49, What model Palomino are you working with? I have a SS-1251 that I am in the process of doing the same thing to it. I wanted to use the black tank as a grey one after taking out the stock toilet and replacing it with a Laveo dry flush unit and sealing off the tank. I can run a drain hose from the sink to the shower line to eliminate the 3/4" drain on the side of the camper but I am still working on how to pressurize the grey water to get it to use the old black tank. A simple pump set up will do it but I am not there yet. Let me know if you have access to your shower drain line and I can tell you how I made it work!