In your case, after the RO unit, will be the "finished product." Just take that finished product line, and plumb it into a DI, then the "out" of the DI will be your new finished product. Everything just runs in line, super simple. These filters use a 1/4" OD tubing, all the fitting are quick disconnects, and the tubing is purchased very inexpensively by the foot at any hardware store.