Ok.. here's our new challenge taking away a sippy cup!! Aayden already drinks from a straw cup. Problem is... when he…

Ok.. here's our new challenge taking away a sippy cup!! Aayden already drinks from a straw cup. Problem is... when he drinks MILK he drinks it when he wakes up (we're in the car), nap, afternoon snack, & bedtime. So therefore it's in a sippy cup. I was putting it into a straw cup but then the inside of the straw gets all nasty and is impossible to clean out. Anyone have any suggestions!? Idk what else to do. He drinks everything else from a straw cup.