My temperature measurement is via a waterproof, solar powered otterbox. It sits on the pool deck with the thermistor cord dropped into the water. This way I can take temperature measurements all the time without having to keep the pump running for accurate readings.
If I were to put the thermistor inline with the sensors, I'd probably just buy another threaded PVC T junction and the equivalent male threaded cap. Just drill a small hole in the cap for the wire to come out, and JBWeld the hole when done.
