I'm investigating a used tank on Craigslist, and wondering how to go about transporting it. It's basically 90 gallons with a sump and live rock, maybe a few fish. I think I would like to paint the back and maybe drill it so I don't need to use an overflow box. Should I try to retain some of the water for keeping the live rock? How do I keep the live rock alive while I prep the tank? Should I worry about whether it's been filled with tap water? I've read in other threads that it can retain stuff that never leaves the tank. In light of this, should I let the rock die and replace the substrate and start from scratch? Am I over thinking it?