To pour a liquid (out of its proper container into s.t.).
If I pour water from the water container into a bucket it is towang but if I pour water from the bucket into a special water container it is isi. Isi has the emphasis on putting into a container while towang has it on pouring it out of s.t.
I have already poured out all the water that was) in the bamboo water container.
You know how to pour water.
Sasangne magtowang kahawa tekkakun.
While she was pouring coffee I arrived.