Go through the No.3 Cloaca Spur where you can use the No.1 controls. Then go back and open No.3 and No.10 again. Then go and use the No.4 and 11 controls and go through the No.4 Cloaca Spur to go and use the No.1 controls. Then go back and use the No.3 and 11. Then head through No.1 Cloaca Spur. There Cuchulainn waits for you.