I-spin, U-spin, and penguin dominance in $B \to K K \bar K$

Isospin and U-spin symmetries are useful approximations for studying penguin dominance in $B$ meson decays to three kaons, $B\to KK\bar K$. We point out certain subtleties in treating these decays in these approximations. Resulting uncertainties are discussed in determining the CP content of the final state in $B \to K^+K^-K_S$, and in relating the CP asymmetry in this process to the value of $\sin 2\beta$.