I know there are a few threads on this topic but none answered my question

1) If im using the "ATO with 2 Sensors" setting do i need to buy the splitter to get 2 sensors on the Level 1 / 2 port??
2) Is this splitter something special or can i get one from a PC place (PS2 splitter for Keyboard + Mouse)
3) Can someone explain to me about the "Leak Detection" mode
4) I have a contactless sensor but not working, is it best to use a Optical and Float or 2 Opticals or 2 Floats?

Thanks