My search has turned up nothing in the way of check valves in the windscreen line. Doubt there is a built in check on the t-connector. Maybe in the actual nozzle assembly but I hate to throw more parts at it. About to hit 100k so I know there's a bit of money headed her way soon. I'll try forcing liquid or air the opposite way to see if maybe something's just stuck. Thanks guys.

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Scott

2005 4.8iS TS/BLK