I fine-cleaned the tank and painted the back with Plasti-Dip. The outside has the rubberized texture that you would expect. The inside is a mirror black finish. This should really make the seiryu stone pop. The plan is to let it sit for at least a week before I install the bulk heads so that the Plasti-Dip can cure and hopefully not peel when I tighten the bulkheads. My PVC source is out of the some the fittings I need--the silver lining is that it will force me to give the Plasti-Dip plenty of time to cure.