Not all rust is equal, but I've had pretty good success using kerosene and marbles (maybe an inch of kerosene and a handfull of marbles, sloshed around after soaking.) There is a screen at the end of the pickup, so you are not totally unprotected -- but not a lot of comfort in that.
You can do a rebuild or partial rebuild by pulling off the handle assembly -- whole thing lifts out including the intake. You would need a gasket to put it back together, and that's easy enough. But that gives you access to the inside of the tank, and can reach in with a tool to scrape the bottom some.
You can also pick up another tank -- wouldn't hurt to have a couple anyway (may end up doing a rebuild or two). I think I'm at a point where I have a couple more motors than tanks, but would need to take inventory to know for sure -- tend to collect them if you run period outboards. I end up using one or two regularly, so have to keep the others in good condition (a little kerosene again for storage).
