If you have any sort of free-standing pail at all, you need a liner. It might be one of those things, like the person who reviewed it in the blog I'm about to send you to, that you didn't know you needed until you needed it (this is true with many products I have found).
The thing is, you have a chance to win one. A good waterproof one that you can just throw in the washer with your diapers from Bum Covered Diapers on Cloth Diaper Contests & Giveaways blog. You can pick your color, and there's a lot to match almost any nursery theme!