Motorcycle Repair: Gas Tank, warm soapy water, rusty tank

Question
So I have many years of fab experience, but I have just begun to work on motorcycles.  I have a really rusty tank that I was hoping to slightly modify but I need to cut it open first.  I was wondering if you had or knew of someone that could help me.  How should I go about cutting it open with out blowing my self and the tank up?
Thanks for any help.

Answer
Jared, there are several ways to ensure that the tank is cleared of fumes.

One is dry ice!
http://www.continentalcarbonic.com/dryice/weld-tanks-with-dry-ice.php

Another one would be to use some mineral spirits, alcohol or acetone to flush out the tank residues, then wash out with warm soapy water. Phosphoric acid, mixed in water in a empty fuel tank will help lessen any leftovers. Leave it outside for a day or so, to allow the fumes to dissipate.

I have been using ZEP citrus cleaner from Home Depot to clean parts and cut through petroleum grease and oils, with good effect.

Bill Silver