"Brian D" wrote in message
news:9Qmfc.39212$wP1.153766@attbi_s54...
It just takes care. If you can, you wash out the tank. Regardless, you
purge it with air for many hours to guarantee it is dry. You fill the
tank
with inert gas such as argon, then weld. Same process if you weld tanks
of
unknown condition or which had unknown contents. Welders do it all the
time.

Once the tank is inerted, I would still be concerned about the residual gas
fumes in the bilges. An area where you can properly perge or inert.

If it doubt, or you can't test it before welding, then the tank should be
removed from the boat.

Steve
s/v Good Intentions