We found a local company that makes tanks (fancier than ours) and they put the fittings in the tank for me. We just marked the tank where we wanted them and they did it. As I recall, it was about $20 including the flange....and I could watch!
They basically cut the hole with a hole saw, then put the fitting on the drill and spun it in the hole. The friction caused enough heat to fuse them together...pretty cool!