With G-d's help, your family has grown, and you would like to use your cellar, below ground level. For the comfort of the new inhabitants, you install sanitary services, such as a sink and a toilet. But how will you lift the waste water up from the cellar to the municipal sewage lines, which are at a higher level?
The standard solution for this is an electric sump pump. When some water is used the waste is collected in a holding tank with a float or an electronic level sensor. When the maximum height is reached the water is pumped out. This is a wonderful idea for the weekdays, but what can be done on Shabbat? Every second time a toilet is flushed, there is a good chance that the pump will go on.
The solution proposed by The Zomet Institute is to install a mechanism for Shabbat that "continues an existing current." Every ten minutes, the pump is turned on for a short time, irrespective of the position of the float. If the pump is not needed, it goes off after a few seconds. But if the holding tank is full and must be emptied, the pump will stay on until the water has been removed, when it will automatically stop.
Thus, a person in the cellar never directly or indirectly turns the pump on. All that he or she does is to contribute to the action of the pump, which goes on anyway every ten minutes. This system can be used without any fears of desecrating Shabbat.
Important note: Installing the Shabbat control system before the sump pump can save the expense of an unnecessary service call, since sewage systems with built-in electrical equipment must be installed by a licensed technician. The Zomet Institute technicians will not open up a sealed system, in order not to interfere with the manufacturer's warranty. For your information, "Amidan" sells sewage pumps with the Zomet Institute Shabbat controls already installed. For more information, contact Amidan, Moshav Batzra, (+972)-9-7441606.
For more details, contact The Zomet Institute.