A 46 is really too small for a tang. You could probably get away with a smaller species of tang but anytime you can use the phrase "get away with" in reeftanks it usually ends badly.
A Sohal is likely too big for a 100 gallon at 4" and will surely outgrow the tank quickly. I'd keep a yellow/purple/Kole in a 100 gallon tank though.
I'm sure you'll get several examples of "How I do it" from people who have successly kept tangs in tanks this small, but I wouldn't do it.
i've got a yellow tang in my 44.. it's doubled in size in a year.. i'm going to end up getting that larger tank earlier than i expected.. =)
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I have a 220 gallon tang tank with a Purple, Powder Blue, Blue Hippo, and Sohal tang...and that's about all she can take. My sister bought a 1" blue hippo tang and put it in her 55 gallon tank about 2 months ago, and the thing has already trippled in size. I don't know how much longer she's going to be able to keep it in that size tank. I think you can put a reall small tang in your tank for a little bit, just make sure you actually have somewhere else to put it when it quickly outgrows it.