Help me design a s/h watering system

[Discus]

I wonder if it might be possible to (fairly cheaply) make a self-starting syphon arrangement out of thin plastic pipe that would result in fairly effective flushing of the pot back down to the level required by SH. Of course, this wouldn't address Ray's concerns over merely diluting the old fluids, but in fish tanks, they say "the solution to pollution is dilution"... So with big enough water volumes, it shouldn't matter too much; more regular flushing == less "stale" solution?

Of course, this does run a significant risk that if the syphon fails (e.g. gets blocked by a root or medium) then your plant root zone goes from SH to submerged, although you could perhaps engineer around this with a very small hole at normal SH hole level.