My previous plumber brought up a 1.5" PVC pipe which is shown in the picture with a cap on it. This is the air intake for the spa. We are not using an air blower motor. The new plumber brought out the air intake valves shown in the picture and is telling me these require a 1" PVC pipe be glued to the end. Basically the end of the air intake valve has a 1" slip. He is telling me we need to remove the travertine, chip down and install a 1.5" to 1" reducer. I've notice the air intake valve also has threads. Any suggestions? The original plumber was thinking something, so there must be a way to install a air intake valve/cover onto an existing 1.5" PVC stub. Help!