Ditto the effort with Brasso first. Can't hurt and I've found Brasso
cleans up a number of metals, not just brass.
I can't agree with paste wax as a protector though. Wax offers little to no
protection to water and in this use, it just
wouldn't hold up. Lacquer might hold up better but if this tub gets regular
use, you ought to just plan on shining it up
every so often, assuming it is truly brass. Chances are, it's not and all
bets are off!