Re: How to clean it..
If it's got the residue crud from fuel in it, the best way is to have it steam cleaned. If this is not an option, some fresh fuel with a carb/fuel injecter cleaner [like Gumout] with a lot of sloshing and soaking until you get it all out. You may have to repeat this several times. If the tank is free of this crud, soap and water with a thorough rinse will do the job. This has worked for me and hope it does the job for you.