the best striper for any thing i have found is zip-strip.
it is in a yellow can and has a black and white logo on it. it only cost about $6.00 per quart and you can get it any where that sells paints i have bought it at wal-mart, lowes, home depot, ace hard ware and other places. i use it when i make a oops on my powder coating and it takes about 5 minutes to bubble up all of the powder and the clear coat. so it would prolly zip the spray paint right off.. it smealls really bad so be sure to use it in a open area. and after it takes the paint off i use a rag to wipe the loose paint off and then wash the tank in ivory or some other natural soap, so you do not have to worry about the soap hanging around to long.. that should give you a clean ready to prime finish.
87 ATC 250es
86 Polaris Scrambler