OK, so here's the answer. Use Brine for water ballast. It can have 30% more mass by volume, so you get way over your max gross weight with the same number of gallons. (A technique used at some of the early Hobbs contests before weighing gliders prior to takeoff became standard practice.)

Then, dump some of the briny water on those pesky leeches, and watch them fall away, as in that classic scene from "The African Queen." Just hose 'em off and win the day!