I have a small greenhouse with a two tank cistern--graywater and rainwater with a pump in each tank--and need to switch automatically from the graywater pump when it is nearly empty to the rainwater pump. All I've been able to find are on/off switches; what I need is the equivalent of a three way electrical switch from one circuit to another.
Does such an animal exist? Any help appreciated.
If a moderator is here, will I be emailed if someone replies? Or do I have to keep checking? Thanks.