apollo1,
spoilers
.
.
.
.
.
.
.
.
.
.
.
I believe the order to click the pipes is 3 1 2 4.
As Glorfindel says, the dog stew is used to lure the umber hulks into the cell. Placing the stew in the appropriate place nets you 18,500 XP which is not bad for a little work over a hot stove
Note that you get the XP even if you kill the hulks first and *then* place the stew.
Kez