20 HP Mercury Fuel Consumption

I am getting a new 12' Pond-Tini pontoon boat and I am putting a new 20HP 4 Stroke Mercury motor on it. I cant decide between the 3 and 6 gallon fuel tank. It will be used by the wife to move around in the coves. Probably go from Williams to Little Mustang and in that area. How much fuel will this motor use. Will a 3 gallon tank get her through a weekend?

Get the 6 gal and you should not have any problems.

that's what I will probably get. I would rather have to much than run out.