Several things to do.
Lift the tank and reroute the drain tube from the tank - on the K2 they had a tendency to run the tube the wrong side of the frame - causing it to kink and not work - run it the other side (search the main site for the solution).
http://www.sv650.org/sv_faq.htm#Are%...filler%20caps?
then add Wynns dry fuel to the tank and run it through
should do the job
I would also check the underside of the tank for rust - not uncommon and at £325 tanks are not cheap!