I've read a number of threads on coolant flush. I'm at 50,000 miles so I figure I'll do it now. There seemed to be a general consensus in flushing three times with distilled water, before adding the new Dexcool. Since its a 22 qt system, we need to get 15 gallons of distilled water for the flush? OR do you just use tap water for the first two flushes and distilled for the last flush. Just figured I'd check before I buy the grocery store out of their distilled water:) . Thanks