One of my overflow rain barrels is lower than the rest of my rain barrels and as a result it overflows.
float valve and empty the barrel from the bottom with a check valve. I took care of installing the check valve a few weeks ago. With that taken care if it was time to install another float valve
1/2" FPTxFPT coupling. I screwed the float valve into the coupling and then screwed the other end of the coupling to the brass overflow that I had installed on the rain barrel.