A Few Questions...

I have an aluminum tank on my V20, she is a 1987 anyone have any idea the fuel cap?
Also, I had to pump out the tank due to bad gas, I am on my 3rd fuel water seperator, because of a what looks like alge, I am gonna go ahead and slap the Racor on her and be done with it, and monitor it.
Also, I bought a Hummingbird Matrix 17 fishfinder, do any of you guys have this unit and if so, where is the best transducer mounting area?,,,,Dirk