2002 cadillac deville

You'll have to drain the tank and clean it out, IMO it's best to just drop it and do that, along with swapping out the fuel pump and new filter. Of course you can just pump out the old gas and use a good gas cleaner and hope for the best. (disconnect fuel line at the filter and jumper the fuel pump to drain all the fuel, be sure to have a suitable container on hand as it will come out under pressure) The injectors will need a good cleaner additive in the new fuel as well.