One of these 1 or these 2 will do you. Infusers shouldn't be overfilled (max 50%) as the leaves expand on contact with water, and also need space to move about a bit while infusing.

Megan's uncles' tea sounds like what my boss tells of tea on trawlers in the 70s: gallon pot of water and about 2oz loose tea onto a low light as you sail, topped up with more water as it was drunk, and more leaves from time to time. By the time of return (about a week) the pot would be about half full of leaves, and rinsed for the next brew. He certainly drinks the strongest tea (and with the most milk) I am ever asked to make.