I think kitchen sinks are 3/8" (but I can never remember). So you'll want a 3/8" female, 1/4" male, 3/8" male tee. You should be able to find one at the local big box, or hardware store.

Something [like this]( http://m.homedepot.com/p/Homewerks-Worldwide-3-8-in-x-3-8-in-x-1-4-in-Brass-Extender-Tee-No-Lead-VETOEMB1B-Z/203444232)

! [Image][1]

 [1]: http://www.homedepot.com/catalog/productImages/300/7c/7cbda008-cefb-4f5f-bb32-b653dfd59289_300.jpg