Personally, I would opt for a sealed connector with water-tight gaskets like the auto industry uses. Wiring to the pigtails, I would solder and shrink-tube over the solder joint for a water tight splice.
I think you can buy the connector pair with pigtail wires at any auto parts store. Just be sure to select a very heavy guage version to accomodate the amperage of the macerator pump....whatever that is.