I flew an old PA 24-260 Commanche B once where the fuel selector and strainer units were located between the front seats.
Draining of the strainer was accomplished by opening the hinged access door located on the floorboard just aft of the fuel selector valve, and moving the quick drain handle to the full aft position. There was a clear plastic tube in the line that allowed you to observe the fuel running out (and more importantly to make sure that it had stopped!)
Never saw any similar system in PA 28 235s.