This is a relatively simple design. You put pump and reservoir inline on the overflow, but before the scrubber. The pump in the reservoir is on a timer so that continuos sump feed pump keeps running and the second pump on the timer just diverts the overflow feed to the scrubber to the outlet of the bucket. Any number of designs are possible, the use of ball valves etc all can be incorporated. This drawing is for the basic concept, any working models will all have to have the flows correctly metered using pump timing etc.