A T fitting with a ball valve and 25 feet of garden hose with a typical sprayer is what I use. It's all spliced in just above the coolant pump. When it's time to wash down the machine, I throw the ball valve, open the fitting for the hose and turn on the coolant from the control panel. No coolant from the normal line loc fittings, just on the hose.
Yeah, the wash down gun option is like 5K...Okuma is higher than giraffe nuts on the few things that aren't standard options, but a 15K 30 Hp spindle and a badass control is standard?...weird but I love that mill.