Two of them here, the 0.75L plastic versions. There is a small round relief valve on the top which somehow fell out of one of our bottles. Camelbak warranty service quickly mailed out a replacement lid no questions asked. Great customer service!

After using them extensively for the last year I am still more comfortable with a 1L Nalgene with a splash guard installed. Easier to clean and less parts to break. I swear the Camelbak has leaked at times -- I've never had a Nalgene leak. So the Camelbaks have been relegated to around the house or town use, and the Nalgenes kept for the trail.