i am into my 6th day with my first go at the master cleanse. yes, i have found my breath to become stale too.
i work in a customer service position, so i have used gum. however, i know a friend who goes on other types of fast on a regular basis. he uses organic cloves which work great on the breath, so i've been using it. you should try it. you can purchase at most grocery stores that have a nutritional dept.