Been there done this man, had a half tank of gas and the seal around the fuel pickup and the bildge pump went out. the cover blew off, we got a ton of rain and a TON of water got in my tank.
Knew the gas was bad by getting a 5 gallon can and filling it up with new gas and just putting the draw tube directly into the can and it ran like a champ. ( i liked this way because this proved it was 100% the gas and nothing else, no guess work)
Now how i fixed it:
1.) couldnt find an electric pump cabable of handling gas so i got a manual hand pump and cranked away at it for about an hour pumping it all into a bunch of 5 gallon cans so i could dispose of it later.
2.) replaced the fuel filter on the line and for me the seal on the fuel pickup.
3.) replaced the spark plugs because heck it was already broken down i might as well, and they are not hard at all to get to. took all of 5 mins to change all 8.