Gray tank capacity - two seperate tanks

We have two separate dump locations - one front and one rear. One of these days I'm going to drop the belly panels and try to see if I can run a equalizer line of some kind. But I also thought of adding a cover for the rear dump with one of those garden hose fittings in it and use a pump and run a hose to the galley sink. But I want to try and make it easier and more permanent then that. Like maybe a pump set up where I can just open a valve and hit a switch at the panel.