Most folks here use Krylon Fusion.
Wash the part that you want to spray in mild soapy water (get any mold release or any other contaminants off), let it dry, spray it and let it sit for a few days to get all the VOC's out. Wash it again and drop it in your tank.
I have heard that acrylics or kids finger paints covered with polyurethane or aquarium safe epoxy works well too.