I use porcelain water crocks for this purpose. For use as a continuous brewer, I don't think the brewer itself needs to be tempered. Just don't make your tea directly in the brewer. Make it in a separate jar, then after it cools, add the makeup tea to your continuous brewer. If you add boiling hot tea to the continuous brewer it may damage the culture.
I prefer to bottle and add makeup tea every 2-3 days. To me that seems the ideal time roughly for 2.5 gal continuous brewers. But since that's about the smallest continuous brewer you could use, if you had say a 10 gallon continuous brew it would probably be more practical to go longer between withdrawal/makeup teas.