Cleaning the tank your self is pretty easy mate. Unfortunate accident caused a fuel fire while i was changing my fuel pump wiring. Any hoo i needed to clean the tank out after from melted bits and bobs. Its only half dozen bolts or so and a few hose clamps. Shouldn't take longer than 15 mins to drop it out. Drain it and go buy 10 cans off carbie cleaner and go wild. Inside of your tank should be clean i would imagine your only wanting to flush out shit that's gotten into tank.
Its pretty simple just make sure that once your done you give it a good 2/3 days dry time after you've cleaned it.
If you've got rust issues i wouldn't risk using even if you clean it.