I filled mine with windshield wiper fluid to avoid freezing and it
worked very well. To fill I made a connection hose from a broken 12V
air pump and garden hose female connector so I could use the tap water
pressure to push in the WW fluid. That gets it 99% fluid and then use
a regular air pump to get the pressure up. Used it for two years w/o
issue, combined with a brass tailwheel. The WW fluid netted 0.869Kg
and moved the CG 6.9%. This was in a 65x210 wheel.