A chemical plant has four tanks (A, B, C, and D), each containing 1000 litres of a chemical. The chemical is being pumped from one tank to another as follows

From A to B  @ 20 litres / minute.
From C to A @ 90 litres / minute.
From A to D @ 10 litres / minute.
From C to D @ 50 litres / minute.
From B to C @ 100 litres / minute.
From D to B  @ 110 litres / minute.

Which tank gets emptied first, and how long does it take (in minutes) to get empty after pumping starts?