Ah …. never one to cast aspersions on anyone, let alone old wives, Her Ladyship (that would be me!) must take exception and debunk an old wives tale.
Does anyone remember teapots lined with tannic – that brown coating inside the teapot? And the rule never to wash out the teapot because the tannin liner made good tea?
The fact the layer of tannin rendered tea bitter doesn’t seem to have mattered.
This is one old wives’ tales that can be flushed.
If your teapot accumulates a light coating of tannin, fill the teapot with hot water, add up to four teaspoons of baking soda, stir to dissolve and let sit for a couple of hours. Rinse thoroughly. Avoid using soap or detergent on the side of your teapot as much as possible, as any lingering taste could spoil the tea.