Yes, Action Park did have looping waterslide. You had to be a certain weight so you would be able to make it all the way around the loop. I do know that many people got stuck in the loop, and that they had a special trap door to get the people who got stuck in the loop out. Action Park, as far as I know, was one of the most unsafe parks ever. It is now known as Mountain Creek.
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Parks for 2000: CP, Great Escape, Great Adventure, SFA, Islands of Adventure, Kennywood