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
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). It' working well so far, a little messy, but she is drinking more and more each day.