Bidirectional tidal flow

[Lampshade]

There's small PVC valves on washing machings for the fill cycle, cheap, but only 1/2" opening.

Using a OM with a timer as suggested earlier would eventually give bad timing...BUT... you can do it without a PLC. Just get 2 adjsutable timers (like Panasonic PM4H), a relay, and a windshield wiper motor. Windshield wipers have a home sensor, or auto off switch. Most have them now unless it's off a 67 VW or something, i used a rear wiper off an aerostar for something similar, cost $10 from a wrecker. If you set timer 1 to run for 15 sec on (or whatever it takes to open). then off for timer 2 amount (your Open time). And On again to home position to reset timer 1 again.