I always thought that boys underwear was called pants and girls was called knickers and if you lived in the States their trousers were called pants 
I'm fascinated by this thread, I'm hoping people are joking here but knickers should be changed daily surely? Or yes twice if you're going out, swimming or similar.
I suppose I could buy a shed load of panty liners to save on washing but that's not good for the environment, unless san pro.
Yeah I'm not sure where I'm going with this really. Time to make a cuppa and keep watching this thread with interest.