Flushing with diesel is a common and accepted method of removing water contaminated oil. Diesel fuel is hygroscopic and will also clean out the old oil. Adding alcohol, can perform the same but is more expensive and any benefit may not be worth the time it takes. It can also add more water if you don't use a "dried" alcohol. (For example, use a denatured alcohol or isopropol alchohol... NOT rubbing alcohol which is 50-70% water.) I after replacing the lubricant, I would run the auger for a while to help vaporize any water left in the system before sealing the gearbox. Did this to an engine which got flooded with water while 4x4ing and never had a problem with rust or other ill effects until I totalled out the truck in a rollover accident about a year later. Other solvents will work too. Acetone, lacquer thinner, carbon tetrachloride, japan drier, etc but much more expensive than diesel and not as safe.