When I had to return to the office part time my son, then 7 months, decided he did not want anything to do with a bottle.  We bought a ton of sippy cups to see what he would use.  We had tried several without success before I tried to drink from them.  I can drink a thick milkshake through a straw, but I could not get any water from a sippy cup with its valve in.  Once we removed the valves from the cups, he happily drank from all of them.  We modified the Take n’ Toss cups by drilling holes in the lids.