Water additives to help with smell?

Awhile back I remember reading in a thread that if you added a few drops of something in your rat's water bottle it would help lower the urine smell a bit but I can't remember what it was or find the thread I read it in.

Do any of you guys add anything to you water bottles to help bring down the urine smell some?

Have heard Vanilla extract helps

I add water to the water bottles and clean tubs twice a week, that keeps the smell down :)

When I started breeding rats I used to add vanilla extract to the water, that was a waste of my time. Like Jerry said, just add water and clean often. I clean every 5 - 7 days depending on smell.