Some answers to things folks have commented on......
The Sani-con mounted macerator pump (Far as I know theirs is the only one designed to be mounted) uses a standard 3" Flexible "Stinky Slinky" hose (About a foot or two of it) to connect to the standard 3" dump port.
Thus, should it fail, you can use the stinky slinky as back up.
As I said before the Sani-Con also has a gray water bypass. this is a small hose that lets water go around the pump.. Slowly. to drain the gray tank if you are one of the people who does likes to leave the valve open.
Far as I know only one company makes the motors for all the pumps.
The macerator pump has two stages, If you look down the inlet you will see the MACERATOR, this can be metal or plastic Two blades (one wing) or four. Below that is a metal plate and below that is the pump part
The pump consists of a rubber Star or Daisy in an oval shaped housing, the inlet to the pump is at a point where the chambers formed by the arms (leaves) of the dasiy and the chamber are fairly large, as the daisy turns the filled chamber is compressed by the oval shape till it reaches the outlet end of the pump. Where it discharges.
This is a fairly common pump design.
HOWEVER if you let the pump sit for months.. The arms of the daisy can "Stick" to the oval .... A slot in the non-pump end of the motor shaft lets you break it free by turning the shaft with a flat bladed screwdriver or coin.