Experimental Results:
Just put my G2 thru its paces last night. This was in a "standard" Simpson 5kg top loader, about 10 years old (if any1 cares!) It survived. Slight water penetration in the tailcap but all got blocked by the slight lip in the rubber pushbutton. Turns on and works okay, beam image is as it was before. The batteries - I was hesitant to use after the wash, but because the compartment/chamber was completely dry (but smelt like the washing power used), I measured voltage and it seemed normal. I forgot to measure before the wash, but the two cells recorded 2.97V and 2.98V after, and with no visible marks, so no worries.
A Surefire G2 (their entry-level light) has been tested to be exceed the punishment of a washing machine.