I've weld-repaired a steel tank before and I can no way be described as a good welder (!) - its no prob if you wash it out with detergent properly.
Its always a good idea to avoid epoxy, except on fibreglass tanks
as modern petrols soften almost everything, and epoxies are a b'stard to do a 'quick' job with anyway !
Anyway - my mate Derek in Capel (just south of Dorking) is an engineer (and ex-racer) who can do smart repairs
Headline Engineering 01306 712565