Sounds like gas is getting into the vent hose. Probably the metal tube inside the tank has been breached somehow, like maybe it has broken away from a spot weld. If you can get into the tank to fix it, you can patch the hole. Otherwise, you live with the leak or replace the tank. It's an uncommon, but not unheard of problem. IIRC, there's a member or two here that have faced this issue. If your bike has an access plate on the bottom, like the B12's do, it's much easier to fix, but as I understand it, not all B6's have this feature since the plate is for a sending unit for the fuel gauge and the '00 B6 doesn't have one.