Legal requirements
U.S. marine sanitation law requires that you be in open ocean at least 3 miles from the nearest point on the whole US coastline or any island to flush a toilet directly overboard or dump a tank.
There is a good use for your macerator, Bob: At least 2-3x/year--and especially in preparation for winter layout, the tank should be thoroughly rinsed out out to flush out any sludge. That doesn't require fllling the tank...only putting enough water into the tank via the deck pumpout fitting--'cuz that sends the water into the tank at the bottom to stir up any sludge and hold it in suspension so it can be pumped out--to cover the bottom to a depth of 3-4"...pump that out...repeat...repeat...till you're pumping out clean water. Or, after you've put 3-4" of water into the tank, turn on the macerator while continuing to run water.
However, if your macerator has sat unused for several years, it may not run any more. If you're never gonna use a piece of equipment, remove it instead of letting it deteriorate and become worthless.