Protecting your (my) passport from liquid damage

After an unfortunate incident involving my passport and some alcohol-based hand gel in my bag, I decided I needed some sort of waterproof passport protection. But searching around for "passport wallets" mostly doesn't result in anything waterproof and all the wallets are large, bulky or ugly. But there is a really simple solution. A 4 mil ziploc bag of the appropriate size. What's the appropriate…