Check the tank vent for a blockage...
A blocked tank vent will cause a macerator to pull a vaccuum preventing more than a gallon or so from being pulled out. Check both the thru-hull and the vent fitting on the tank...scrape anything you find out with a screwdriver blade.Btw...I'm guessing it isn't on either Lanier or Allatoona--that it's on the coast somewhere....'cuz a 410 is a LOT of sailboat for either of those lakes. But if it isn't in the ocean, you can't legally use the macerator to empty the tank anyway. Enforcement on Allatoona is a bit lax...but VERY strict on Lanier. It's illegal even to have a macerator installed or any toilet or tank plumbing connected to a thru-hull. The DNR randomly inspects, and it can cost big bucks in fines if you're not in compliance.Just thought I'd mention it.