1993 Toyota Camry Possible oil and water in gas tank

Engine Performance problem
1993 Toyota Camry 4 cyl ? Miles

I believe my girlfriend put lawnmower gas mixed with oil in the tank when it ran out of gas.

After putting 6, 7 gallons of gas in, the car will run for about 20minutes, then losses power and will quit running altogether.

Is there any other way to get oil and water out of gas tank, besides dropping the tank? And if not how to clean tank out after it is dropped?