This will not work because these sensors are not water proof.
You can attach this type of sensor to the tubing and fix it with some aluminum foil and tape as isolation against the ambient temperature.
Accuracy should be quite decent. We used something similar for many years in the aquaduct series (external cooling unit).
OK, will do. In fact, I actually have some aluminum tape that should do quite nicely to attach the sensor to a fitting, then wrap in a few layers of electrical tape.
I doesn't even have to be a fitting - any metallic surface in contact with liquid will do. I've tested this method on waterblocks, radiators etc. The thiner the metal, the better but since there is lot of thermal inertia in any loop it worked quite well even on a thick wall of an aluminium Aquatube reservoir.
And if you don't mind some 20-30 seconds lag in temperature reading it can even by a PVC/Acrylic tube.
Also, I would focus on a propper contact with the metalic surface and would't bother much with thermal insulation unless your sensor receives some airflow where it is mounted (but then it means that You should place it elswhere anyway