Going out to eat: Fast Food: Filling your drink at the Fountain

This is a challenge and something that you think will not be a challenge but it is.

What I do is hold my cup with my left hand that needs to be filled at the fountain. When the weight of the fountain drink cup fills up; I change hands and use my hand hand to hold the drink. I then use my left pointer finger to push the drink of choice.

I then only carry the full fountain drink in my right-hand. The weight is too heavy for my left.