OK, I have never done this and I'm just theorizing. Don't try this unless it sounds like a good idea to you. Better yet, wait and see if some other people in here blow big gaping holes all in this.
You want to try it to see if it the fuel is OK, right?
So, filter it good from drum to drum (someone above suggested the right filters to use).
Empty your Racor
and fill it with the newly filtered fuel. If it runs OK, you're golden. If it diesn't run at all, you got some lines to flush and prime. A pain, but better than a tank full of bad fuel. If it runs, but just not up to snuff, mix it in your tank with new fuel. 50/50, 25/75, whatever seems right according to the performance you got.
While testing, remember, it takes a while for the fuel from the filter to get to the engine
, probably different for every engine. If you put the fuel in the tank, at idle it could take an hour or more for the fuel to get through the Racor
and to the engine, depends on how many GPH you burn. I had my mate accidentally shut the fuel off on one engine. We were almost a mile from the marina before it cut out. (That's twin 3208Ts which suck fuel compared to a sailboat powerplent)
If it was me, I'd rig up a fuel polishing system and pump it back and forth between drums until the filters ceased to clog, and then mix 50/50 in the tank, but that's me taking the risk, not you. I wouldn't do it to someone elses boat.
OK folks, tell me where the flaws are...