bathroom breaks

I pee every 2-3hrs which is freaky and annoying. Im just wondering, particularly on the trips in the South Island where you are say going from Queenstown to Milford Sound etc between big towns, how often does the bus stop for bathroom breaks?

I know that the buses have restrooms on board but they are only for emergencies, and tiny and fill up quicky as i experienced on one tour in melbourne..not good.

Dont want to spend the whole time wondering wheater i can wait hours or not..coz most of the time i cant... Esp when you got your period and its not good or normal...

Sorry to bring up this embarrashing topic.