I had one...... great boat! I miss my old Fisher....... Does your boat have the aluminum decking??? That was one of the best things.
I do believe the tank is 18 gallons or it was on my Fisher GT with the same exact motor.
Welcome to iboats.
Post a few pictures!!!
there should be a plate in the deck over the sending unit for the tank, and typically, there is a plate on the tank with capacity and other info.