Both the WL500 and WL300 can be used to implement this application
In case you have available connection to the public water system, the automatics can be installed as a level indicator, to know the level of water in your tank.
Place the floating and the contaniner together, one onto the other, placed to an aproximately height of middle of tank, and wire cables red and white to a low consume bulb lamp (prefereable neon). This lamp will turn on only when water level has reached below your setting (the floating and container, see figure 1 below) and will keep turn off while water level is over your setting.
diagram of a level indicator using WL-300
Install Wl500 as indicated in the box (see technical details at this site) and then connect cables as indicated in the diagram below
diagram of a level indicator using WL-500