The K-305 Rite-Temp Diverting Shower Valve is designed to be used with a showerhead and tub spout only.
The bottom port is made for a non-restricted flow spout. It is not recommended to connect restricted flow devices such as a deck mount spout, body sprays, handshowers or diverters.
Use only 1/2" copper pipe between the valve and tub spout. Using other pipe materials like PEX of PVC will cause back pressure due to narrower internal diameter resulting in water flowing from the tub spout and showerhead at the same time. Any restriction between the valve and tub spout will cause unsatisfactory performance.