I'm not quite sure why you are having so many problems with your sippy cup leaking. We have used at least 20 cups in the past two months, the 10 oz Nuby sippy gripper cups and the only time they have leaked is when we didn't put the lid on correctly and didn't line up the grooves and notches on the spout with the lid.

If you are filling the cup with formula or juice and are shaking it, you should be able to tell where the leak is coming from. I have tried to make the cups leak and they still don't leak.

It's possible that the batch you bought your sippy cups from at Walmart may have been defective. You might want to try writing directly to Luv n Care, the manufacturer of Nuby Sippy Cups or calling them at:

2805 Saint Charles Ave
Monroe, LA 71201
(318) 388-4916

They have always been courteous and helpful to me.

In fact, my family and I like Nuby products so well that we now promote them at : http://www.nubysippycup.com

Hope this helped.