This is pretty funny, since I am quite conservative in what I would consider appropriate dress for a child and I wouldn't give a second thought to allowing a child to wear a tank.
(sorry, I am new and don't know how old your daughter is)
However, my brother's children attend public school and they ran into an issue of girls wearing the noodle strap shirts (tended to be thinner and more revealing). Then came the arguement of what is noodle and what is tank? How wide do the over the shoulders have to be?
The school finally just said "sleeves!".