I got mine
here. and I cannot imagine being without it now. It was IMO the second best purchase I made for my tank (good skimmer being first.)
It COMES with 2 float valves and there is nothing to build and it can be used in a few different ways. I use one valve in the sump to turn ON the ATO when the level decreases and the other valve in my top off water container to make sure it doesn't run dry and ruin my pump.
I
<3 it! I highly recommend this ATO.