Bathroom Elimination

In our family I clean the bathroom.  I typically do this on Sundays to get ready for the week.  The last 2 weeks, our bathroom has been particularly icky.  I've decided I'm going to do an elimination "diet" for bathroom use to determine who the offending part is.  There's only 3 of us, so it shouldn't be too hard.  Oh wait--we only have one bathroom.  Hmmmm