How did Tobi suck in Foo using Kamui without touching him?
This can't be possible since Tobi must materialize and touch his opponent in case he wants to absorb him. This is a mistake that was made by the animators. See the quote below from narutopedia: 


  Occasionally, in the anime, when Tobi goes to absorb his opponent he does not touch them, this is a mistake that the animators made as in the manga there is always bodily contact. A notable occasion of this is when Tobi fights Danzō's bodyguards, he does not have any physical contact with Fū when he absorbs him.