Hopefully it goes without saying to never use tape inside the tank. So you are left with what to secure the probe? Most people use hot melt glue but that stuff gets really brittle over time in my experience. It will eventually get knocked off. Dont risk it keep the thermostat probe on the outside. Now I do use glue to secure thermometer probes and they last a few weeks or until my snake decides to remove them but there is no risk if they get knocked off.
I made the mistake of having the thermostat probe in the tank before and it did get moved and the UTH was 130 degrees. Snake was no where near it but a close enough call that I wont ever try that again.
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