I put a little TTO in mine, but what keeps the smell down best is just closing the lid. Most of the time we leave it open and the smell isn't bad, but after a day or two of diapers it starts to smell more and we just shut the lid. Not sure if that helps much; sorry.
I try to keep the lid open as this keeps the pail itself a little less smelly, although the smell that IS there can be smelled in the room with the lid open. I've noticed that by running the ceiling fan it helps to make it not as noticeable.
Re: How do I keep diaper pail smell at bay?
I just started using Diaper Dust and think it has made a huge difference.