A steel air compressor tank, or propane tank will stand the heavier vacuum, you could try a water heater, but that's iffy. A vacuum cleaner will not develop much suction, but any gas engine is a good source for higher vacuum, even some diesel pickups will have a vacuum pump for the brakes. Or a refrigeration service vacuum pump, intake of air compressor, junk fridge compressor. Not much volume is needed, as you're not pumping air , you're only building the vacuum and then the volume of grease is relatively low.
The next part would be a hose that could stand the vacuum, spiral PVC suction hoses, wire reinforced hoses, possibly hydraulic hose?
If the gearbox has seals on the shafts, it may be possible to pressurize it with air to pump the grease out. In that case the hose wouldn't have to stand vacuum, or very much pressure either, 10-20 psi would be more than the force of vacuum.
Either way, heat would help a lot.