How about a little more info...what exactly are you trying to seal?
I ask because just sealing a pin hole leak from the outside is a stop gap measure at best.
Pin holes develope from the inside out.
Generally in the back bottom part of tanks..where water and other contaminates sit...until they rust thru and create a leak.
Best way I have found is to weld them up with a mig or tig welder and then clean, acid etch, and reseal the tank.
I recommend POR-15 as the internal sealer.
Done right its never a problem again.
Epoxy sealing from the outside? works sometimes, and sometimes not...might hold a day, a month or a year...but generally not a hell of a long time...
Just my two cents.