Drawing below of a single flower pot type of setup with its own loop siphon. Siphon must be reliable 99.9999% of time otherwise it is useless and not practical as a water controlling device. This loop siphon below is a conceptual and as rule of fluid dynamics should be able to cutout without problem (touch wood).
It will be made from 15mm or 1/2 inches PVC tube all the way, with an enlargement to make the down spout bigger to reduce it effective length hence making the length of D less than C.
Flower pot below is ideal for this project. Hole already there, just hook a siphon to it and you are done.