Fuel system cleaning, passenger car.

[BTR69]

Good morning. I hope it’s OK to post about a passenger car in this particular part of the forum. Not a tow rig, but these cars did get us back-and-forth to the dragstrip a few times.

Looking for suggestions on how best to clean out a fuel system in a passenger car. I have a 1999 and a 2001 Buick Park Ave, which both have not run in over five years each. I’m hoping to avoid having to drop the gas tanks to clean them out. Any suggestions on a good way to clean the fuel lines without dropping the tanks? Trying to put as little work into these as I can to ensure they do actually run before putting any real effort into making them reliable vehicles again. Thanks.