Gas it too dangerous, and it is too volatile. It will evaporate too fast skewing the results.The gas will creep through the tiniest crack, that will make no-never mind to a running engine. You will be fighting a non-issue for days.
Kerosene or diesel molecules IMO are too big, and they leave behind an oily residue, plus they stink. But they may/will work overnight
Common parts-washer solvent works just right;results in 20 minutes.I have not found a better commonly available test-fluid.
Paint thinner, the more purified form of washer-solvent will creep almost like gas, so I stay away from that too.
Water-molecules are way too big and they stick together like glue. Just try pouring water through a tiny straw...
I don't actually fill the chambers.I only cover the valves, or the perimeter of the valves. I watch for the creep, in the ports.
