Water sensor placement on a 4 chamber sump

[ReefOC]

I have a Hydros water level sensor, and don't know where it should go in my sump. My sump has 4 chambers (1- inlet from tank. with Filter socks, 2 - Empty, 3 - Protien Skimmer, 4- Return pump. The water sensor has 3 levels I think. Thank you in advance!

 

[KrisReef]

I put mine in the pump chamber where the evaporation shows up first.