Okay, I'm going to get arguments here but I'm only passing along what I was told by the mechanic who comes to service the emergency generators where I work.
I noticed he had several cases of windshield washer fluid in the bed of his service truck, five cases, four gallons to a case, and asked him why he carried so much. He told me they put it in the fuel tanks to evaporate the moisture from the deisel fuel. He said it is the same as HEET, and cost a lot less. I asked "what about gasoline engines?" He said same same. The alcohol in the washer fluid evaporates and takes the water with it.
Okay, I'm ready for responses on this one. and it's not my opinion. The guy works for Onan, a big manufacturer of generators and other engine powered equipment.
Tom