I spoke to a retired Marine Corps armorer at a technical school some years ago. He mentioned that they had cleaned weapons in aviation gasoline and live steam, and I suspect that is what is in the tank (gas, not steam of course). I asked him if that wasn't dangerous, and he said they did it all day along and smoked whie they worked, no problem. Note that the rifles are going in the dip intact. There would be no reason to apply stock finish to metal, and no reason to lubricate wood. By dipping the weapon in gas, and setting it off to drip, you could get a head start in breaking down fouling, grease, sweat, blood or whatever. This pre-soak would make a pile of guns easier to clean later. The Marines would be hitting the beach and firing their weapons heavily witout a lot of time for maintenance. I'm sure they were a mess. You wouldn't have to dip too many before the fluid was stained a dark color. This is all just speculation on my part of course.