Restaurant tea is often "soapy" / "oily" tasting, or just plain bitter, because they leave it out at room temperature all afternoon, and they're using dispensing urns that haven't been cleaned since about 1958.
I don't like mine as sweet as some people. In a 3-quart container, I use a 1/8 cup scoop a little less than full, which I'm guessing is about 3 tablespoons (I should check, huh). I use a Mr. Coffee machine. I just got a new one this week -- brewed my first batch with it yesterday. The one I had was over 15 years old and it was on its last legs; the one-way valve was sticking, the switch was dodgy, and the outlet valve on the brew basket broke a couple of months ago. And it was so old it was impossible to get clean; I was on my 4th or 5th pair of replacement pitchers and was about due for new ones. Those polycarbonate pitchers look nice when they're new, but ice cubes scratch them and after a while they just don't come clean anymore. The new machine uses pitchers made from a different plastic (translucent, more flexible), which I hope will be easier to keep clean.