Sorry Grizzler, had read it too quickly missed out on a few bits. Had you seen the finished job, was the person who was de-icing happy with it, did they say anything, are they long out of training? To be honest if i was doing it, there would have been 320ltr on each wing, not including the tail and fuselage but then i have always been very cautious. If you are concerned i would refer it to whoever is in charge of de-icing operations at your workplace
Yes i have heard of hot water de-icing, never saw it happened but as far as i know its used in some areas.. sounds risky, but to be honest you can blast the snow off for minimal cost (as airlines want this) then give it a quick spray with de-icing fluid, could probably save a a couple of hundred ltrs by doing it.. but it could leave you with one slippy apron...