Ok, I am going to be replacing my Walbro 307 pump with a Walbro 340 (my old pump is 8 years old, and the car was sitting with only 5 gallons in the tank for 6 years ). The car runs, but im getting random knock, and im thinking its rust in the tank and/or the fuel sock is clogged up. When I remove the tank and drain it, how can I check to make sure theres no rust in there? Also, whats a good way to flush out the tank of any rust/dirt thats in there? Is it ok to fill it up with water and just drain it out (they are plastic-lined in the inside right??)...