As a couple of people have already pointed out, if you want an electric holding tank
discharge pump the Sealand 'T' pump is the way to go. It's a bellows based pump using two joker valves that they call 'duckbills.' I've installed a dozen or so over the years, never a failure. They can dry prime higher and seem to do a better job of evacuating the than the 'macerator' design does. Gravity is best, of course, and manual pumps almost never fail, but we have a T pump on ours based upon customer success and we're happy with the decision.
For the person who asked about onboard treatment systems like the Raritan
Type 1's (LectraScan/Scan, Purisan, etc) they are legal
in all waters except those designated 'no discharge' by the EPA. While you can't use them on the Great Lakes
and the Keys, most but not all waters in between are fine as of this writing. The Raritan
website has good info on this.