AFRAID to waste BM when "diluting" for weaning - please help!

At the year point I stopped worrying about "reusing" liquids. I figured that her immune system is more mature than when she was an infant, and there's no way she is going to finish any liquid in an hour (she is an all-day sipper type). So once we went to sippies, I stopped pitching liquid after an hour, or I would be dumping her sippy all day. I have a couple of friends with kids who like to drink their milk throughout the day, and they do the same. I do put it back in the fridge when it's not in use though.