Hose under aux water pump???

[BriceW at webtv.net]

There is a big hose directly under the small coolant hose from the aux.
water pump. I just discovered that this hose is totally rotted with a
very big hole in it.
I have looked all through the Bentley and cant find this big hose
anywhere.
The rotted end connects right under the aux. water pump small hose at
base of he engine. I cant tell where the other end goes yet.
Where in the Bentley is this hose? What is this hose?
Doing a simple MFTS replace has uncovered a host of problems. First the
broken brittle neck  on the aux. water pump, then the tear in the upper
radiator hose and now this.
Whatever this hose is it looks like it has been rotted through for a
long time.