That's almost exactly what had happened to mine except in my case I didn't have a kink. There is a hole under the flap, its purpose is to drain out any excess fuel or water which is sitting in the rim. That was clogged up with god knows how many years of crap and when it had been raining the water that got under the cap went into the tank.
Its a bugger of a job to do but the good news is now that its done, the bike is actually running better than it was before I even noticed the problem.
1999-2000: Aprilia RS 50, 2000-2000: Suzuki TS 50, 2001-2002: Kawasaki KMX 200, 2002-2006: Yamaha Virago 250, 2007-2009: Yamaha Virago XV 535, 2009-2012: Suzuki GZ 250 Marauder, 2012-present: Kawasaki ZZR 600
"Green is better, I need green!" ~ Max my 2 year old