[V8] 1990 v8 over flow bucket.

[chris brown]

When does the bottom hose on the coolant overflow bucket let coolant into or out of the engine? The radiator has a upper and lower hose on it  so im not really sure why there is the 3rd hose into the block off the bucket? 
 the reason im asking this is because my bucket cracked and i had to drive it to work today and it was pouring out that back hose by the time i got to work. (temp was fine)  thanks