Commercial macerator or homemade from garbage disposer

For those that use macerators, is there ever an issue of the black tank not enptying well? I always thought it was important to have plenty of water in the tank so the velocity of it going out the drain would carry the solids with it. Even with the pump, it doesn't seem to me that the velocity of the exiting waste would be anywhere near that going out an open 3" valve and solids would be left behind.