I'd be interested in views as to whether a macerator pump should be
installed higher than the holding tank.

Background: On my boat, the macerator (Jabsco) is installed on top of
the waste tank (about 2 feet high). Although it's supposedly
"self-priming", it only functioned if the tank was completely full,
and then it would only take out a gallon or two. Ultimately, the
impeller self-destructed.

Armed with a new impeller, I am now considering installing it at the
same level as the base of the holding tank. I'd think it would then
be more likely to prime, and actually pump. The only down-side I see
is that it would be constantly "loaded" with waste (unlike now, where
the residual waste presumably drains back down the hose to the tank
level). But if the pump seals are good, I figure that's not a
problem?

Am I missing anything?

I'd appreciate any views.