I wish to detect when the bath/shower plastic drain pipe has warm waste water running through it.
I don't need to accurately know the temperature of the water simple that it is present/not present.
My first thoughts are to attach a DS18B20 temperature probe to the underside of the white plastic waste pipe using some sort of thermally conductive glue (any glue recommendations?) and look for a temperature change with a RPi.
Maybe that is over kill, any better ideas please
Oh and do metal waste water pipes exist?