Good strong tea is fine, I have heard that Earl Grey-types are no good but haven't tested that. Same for "herbal" types - not enough tannins, I guess.
I used 2 bags in 1/2 liter of hot water; leave teabags in until the brew has cooled.
If your water is alkaline you may get a browner result than I get with Norwegian tapwater, which can be quite acidic at times. If so, adjust pH with citric acid (think "lemon"). Put print in, agitate, watch. Sometimes the toning works faster than the staining, maybe it depends on the paper. You can get pink highlights and blue-black shadows, or shades of brown, or tan highlights and almost neutral blacks.