If you have dual tanks I assume you are talking about, usually, the front tank overflowing when you remove the gas cap. It seems to happen with either tank but the front tank is more common.
There is an automatic selector valve mounted on the inside of the frame right about at the driver door. It switches internally between tanks with no electrical input of any kind. There are electric fuel pumps in each tank and the the valve switches internally by pressure from whichever tank you have selected on the dash switch. This unit malfunctions and instead of routing return fuel to the same tank you have selected it returns to the opposite tank overfilling it. The valve is kinda hard to come by and is expensive to replace. You cannot get one at your local auto parts store (no matter what they say) it's a dealer item only...if they can get it. Last I looked it was around $200.00.
You can replace the unit with an electrically operated one for less than $100.00 but you must do some re-wiring, replace some fuel lines and adding in filters to accomplish it.