Adding a sump in tank

Some additional reading tells me that a radiator shop can do a clean to remove the fuel residue. Not sure if its safe to weld after that or not. Im going to give the local shop a call tomorrow and ask for a price to do that and then a price for them to add the sump and leak test it. That sounds like a safer method, have to see what cost would be. I'll post once I get a quote.
Rodney