I realalize that the easiest way is to fill 'er up but I'm going to have to replace the sending unit and I'm trying to keep it as close to empty as possible. It's been over a year since the tank has been completely filled up at the gas pumps. I normaly only put about 20-30 bucks in it at a time. Anyway how can I tell what size tank I have? It's a '79 that came with a th350/203 and a 400ci. Thanks for the info.