Some systems may include two pumps to empty the tank. In this case, the two pumps often alternate operation, and a two-stage switch serves to energize the on-duty pump at the first stage and then energize the remaining pump at the second stage. This second stage action is in addition to any triggering of other system changes as noted for a single pump installation. In this way pump runtime is shared between the two, and a backup pump is provided in case one pump fails to function.