What Should I Do If I Mistakenly Put Some Diesel Fuel In My Gas Tank?

The best thing to do is carefully remove the fuel tank and drain the tank, unhook fuel line from carburator or fuel injection and use something to catch the fuel and crank the key, remove and replace the fuel filter.  Put everything back together and fill tank with "gas" and start. It should be fine . It will be hard to start at first. If the engine has not been cranked you do not have to remove the fuel line or the fuel filter. Be safe and get someone with some experience to help you.

The first thing to do is get the fuel out;  Remove the fuel line, extend it with a rubber hose or something, and run power to the fuel pump.  The best place to do this would probably be at the fuel filter.  The electric fuel pump will pump enough fuel out of the tank to allow the engine to start.  It would be a good idea to run the tank dry, fill it with another gallon of gas or so, then use the pump to remove that gas/diesel mix also.  Fill up with gas and you'll be fine.