Old gas in '78 Dodge van

Hey guys, went up to Denver today with a friend of mine to check out an old 318 Dodge van. We tried to get it started but the owner said it sat for around 3 years so the gas is in pretty bad shape; it would start and run for a couple seconds if we poured gas down the carb but the float bowls would not fill up. We came back and got a new fuel pump which we're going to put in tomorrow when we go back but I was just wondering if there's anything else we should do to make sure it will stay running. I'm thinking I'm going to disconnect the fuel line and try to let it drain the tank a little (there's some fresh gas in the tank) but I don't know if that will be enough.