I’ve never seen a fat pumping operation over such a long distance, especially outdoors, but here are a few ideas:
The bigger problem will be maintaining a temperature > 15 °C over the 300-400 meters in order to prevent the fat from solidifying and jamming up the pipe.
This factor alone could stall your operation, unless you can set up a feedback loop of warm methane towards the plant to preheat the fat in the holding tank using a gas boiler.
To do so, calculate the heat balance between the methane produced by the additional input of fat on the bioreactor and the calories burned to preheat the fat.
Depending on the scope of the project scope and the financial resources at your disposal, if you need to transport over a distance like the one mentioned above, you could use a double buried network (natural protection against freezing) with one or two (for added security) lobe pumps, like the Putzmeister concrete pump, for example. This sort of equipment is in my opinion well suited to your operation. If you apply the proper maintenance machine, use a high-pressure pipe (place manholes at the HP pipe fittings where they are the most fragile), maximize straight lengths of pipe and “wide radius” elbows, and, if you can smooth out operations to ensure continuous transit through the network…your will be pleased with the results for years to come!