I don't know what a Johnson tee is, but if you want to replace the "standard air gap" for you DW, you don't need anything except the OEM hose that came with the machine. The only reason to use a special air gap is if local code requires. All you do is loop the hose so that the top of the loop is higher than the top of the DW, being careful to attach it (usually to the underside of the countertop) in such a way that the hose can not kink. It drain end connects to the disposal if you have one or to the sink drain using a special tail piece if you don't have a disposal. The loop prevents the washer from gravity draining.