This Water Softener 3/8" Hose Air Gap Kit is glued into the tap of the stand pipe.
It enables a 3/8" connection with a air break. This fitting can be glued onto the top of the 1½" stand-pipe.
When you connect the drain to the waste system you must protect the water softener and the water supply from backflow.
The waste pipe is classed as a category 5 risk (sewage) and therefore it requires an air break. A non-return valve on its own is not enough.