when did you introduce the sippy cup?

MamaBear🐻🌼 • 26, Mom of two-proud Navy Wife & SAHM
My little one is almost 6 months..
When did you introduce a sippy cup and why?
I pumped some milk for his cup and I want to let him practice it every day.. but it takes me forever just to pump 2 oz!! 
What do you put in it? No water right just milk? 
This was his first try, he chewed on it lol. Anyone's bf baby never even have to take a bottle? That's what I'm hoping, he will go strait to cups!