You kind of have to find the top they they like, but your DS may be a little young yet, so just offer it at each meal for now. then if he has problem getting water out, change it. Take the little flow regulator out, I find them too hard when they are little.
I actually dont give L a sippy. I hold the cup for her and let her drink that way. It works for us, though independant drinking will take longer. I was advised as L was biting me and the LC thought that the sippy was confusing her as she bites the sippy bit (and hence thought it was ok to bite me
). It' working well so far, a little messy, but she is drinking more and more each day.