How can I prevent tea stored in a thermos from oversteeping? I would like to brew a pot of tea and store in it a thermos to keep it hot overnight so I can drink it before getting out of bed.

I've tried this approach and found that although the tea tasted fine freshly brewed, by morning the tea is extremely astringent, as though it had been boiling with the leaves the whole time. 

My assumption is that, although I had made some attempt to strain the tea before adding to the thermos, enough of the tea dust became suspended that it continued brewing, releasing tannins, and turning the drink very dry.

What are some ways I can cut down on this effect? I've thought of brewing loose leaves instead of bags, although I know there will be dust there too. Perhaps I could strain through a more effective means than the tea bags or tea strainer? Or maybe I should cool the tea somewhat before adding to the thermos?
As posted in comments by members of the community (and adding my own), several tips can help you get good warm tea in your thermos at wake-up:


Choose loose leaves instead of tea bags to avoid tea dust that would overinfuse your tea in the thermos. The small amount there is in tea bags, is heavy enough to sink to the bottom very quickly, so if you pour the tea slowly into your thermos, you can discard it. You can also rinse the tea before brewing with cold water to help expel any excess dust, or (as done in many tea-drinking countries) throw out the first cup of tea made with new tea leaves.
If you're just using tea bags, why not just keep the thermos bedside and then toss the tea bag in in the morning? 
You could try heating cold-infused and strained tea in the evening and put it into the thermos; it has a brewing time of 8 to 12 hours, so you'd have to start this around noon. If you have a microwave close enough to your bed, you could also use cold infusion to make your tea during the night and then give it a blast in the microwave in the morning.