A tablespoon is a non-scientific but very widely used unit of volume, which works very well in cooking, herbal medicine, etc. It is represented by a capacity of one tablespoon which varies from roughly 15 mL in the US to 20 mL in Australia.
1 If tea is properly stored, it can potentially last up to a year for green and black teas. White tea lasts about six months before it isn't as good in quality as when fresher. Stale tea (or bad tea) will taste flat, as if you're drinking paper.  Glass or ceramic containers are fine provided that they're opaque.
view iced tea infusion pitcher on Amazon. The jars with the tea bags or leaf tea basket now go into the fridge for at least 6 hours, and up to 12 hours. I often put a couple of jars in the fridge at night, and it is ready in the morning. Or, if I make it in the morning, it will be ready in time for dinner.