it sounds like you might need a multistage system, an inefficient "air pump" that sucks up water into a teflon impeller, which then moves water well non contaminated after it is "primed"
I think most liquid capable pumps will wear pretty hard with dual use, especially with non contaminating materials (i assume plastics).
Like aspirator -> bulk pump. And it would probably need sensors or a sensible operator to function as it ought to. It has to know when to switch pumps. In this case you would also need vortex control (at the suction hose) and AIR TIGHT connections. By vortex control I mean a little whirlpool will form where you are sucking water and allow air to get into the system, giving your pump an embolism/losing prime. You will need a way to make the inflow of water into the pump hose laminar, using mesh/diffusers, and possibly poke the whirlpool with a stick (stirring in reverse with some kind of tool). I have done this before as goofy as it sounds around big pumps.. we had a guy stand there pretty much and just stir water around the pump intake hose with a long pole LOL
. Only need to worry about this if the water level gets low, but its imporant to consider if you wanna totally drain something. You can pump slower as the water level gets low to get around the "lag time" of the diffusers etc. Then you need a squashed intake too, to keep it bellow the water level. Or tilt your container.
Since your application seems rather small scale, I wonder if you can suck up water using a quality hand aspirator to keep things simple. Or even a large syringe, as goofy as it sounds. You only need to pull enough to flood the main pump. Or, just use a bucket/large cup to flood the pump.
or, if you feel comfortable, you can run the greasy water through some sort of filter.. but idk if this is good idea for aquatic life forms. maybe.