It’s easier for the pump if it doesn’t have to lift the waste. The Grocco design is great - until you need to service it. It’s seen Jabsco pumps screwed into tanks on the bottom. That would work well unit you have to service it. My design is above the tank and works well but sometimes I blow an impeller up from running dry (not priming or running too long on pumpout). But servicing the pump is a cleaner operation.
You're right, it is easier to push than pull. Although the distance we're talking about here doesn't have much impact on the pump. But, yes, it would technically be easier on the pump.
I've had LOT'S of experience with transfer pumps mounted either on top of the tank (tanks with a dip tube) or a few feet from the tank on the bilge floor - those work really well with no issues. To a lesser extent, I've had experience with "regular" macerators mounted in a similar fashion with no issues, either. But I'm sure there are cases, like yours, where you once in a while burn an impeller when using a "regular" macerator.
Another experience with a "regular" macerator used in a not-so-normal way... On my last boat (a 28' Sea Ray cruiser) I wanted to be able to do pump-outs at home. My first "version" of this was simply screwing a regular macerator directly into the pump-out deck plate (about 4' above the tank). That worked well for a couple years till I came up with a more convenient version.
