if someone poured water and cooking oil into my gas tank would i need to replace it or can it be fixed

"If" someone did that it would be bad- since you already tried to start it, that is WORSE- all that stuff would be up in your fuel system now- if it had just stayed in your gas tank, you could have dumped the tank and cleaned it- but now, "If" that happened, it will need serious, expensive professional help-

A de-icer will mix with any water (depends on how much water there is) That will help that go thru the fuel system. Add an octane booster, and that will break down the oil and it will burn thru the system. It all depends on how much crap got put into tank. If it's several gallons of the water and oil, I would agree with tennisshoes. If it runs, burn it out. If not, drain it out like he suggests.