I used carb cleaner, Gas, Diesel and even alcohol. Dont forget the pumps. With the bottoms off, turn on the pumps. feel them work. Then turn the switch to AUX, and feel the AUX pump work. Then put some freash diesel in the tank, and put the pumps back togather. Disconnect the hose from the input side of the first filter, and direct it to a glass jar. Turn on the pumps. Fill up the glass and take a look see. Clean fuel? Then good. Not? then more work is required. Some of the other should chime in. I have no experience with SEA FOAM, but it sounds like something to add to your fuel system, to help clean it out, and keep it clean.