exhaust help!

I got a new exhaust put on my truck last month and i painted the tail pipe gloss black and it looks really nice.
i used 500 degree paint and it just pealed off within the frist week so i painted it again and something happen... i later found out it was pealing off because before i painted it i was wiping it off with paint thiner and the guy at the auto store said thats why it was pealing off. so the next time i painted it i just used a damp rag and now a week later all the paint is slowly coming off. WTF!!
any ideas why???

 

best way i have found to clean an exhaust tip for painting is use steel wool and a lil semi coarse sand paper, and go over it good. wipe with laquer thinner afterwards. then prime and paint. if you are just wiping with lqquer thinner....you arent really giving the paint a surface to stick to.