This fitting is perfect for connecting clear tubing to new/first PVC tubing installations with glue recommended on the PVC end. Select inlet and outlet diameters according to installation. For Inlet should use a clear PVC tube which is 6 or 10 mm (1/4'' or 3/8''). For Outlet should use a PVC tube which is 21 or 40mm (1/2'' or 1-1/4'').