I discovered this to my dismay when building a simple cutoff switch for my fish tank's pump. The pump would turn off/on, water would back flow into the reservo

I discovered this to my dismay when building a simple cutoff switch for my fish tank's pump. The pump would turn off/on, water would back flow into the reservoir, turning the pump back on. The pump cycling then caused waves to hit the float switch. It would cycle on/off at about 1-2 Hz. This was built before Arduino's and Raspberry Pi's were around (and the environment is humid), so I devised a fairly simple mechanical solution of just enclosing the float switch inside a pipe that had a small hole in the bottom. The water level inside the pipe would change slower than the real level, providing the needed hysteresis.