Trying to get a 2005 Chevy Equinox repaired. We just repaired the head gasket and are now putting it back together. Some of the pieces were rusted and had to be replaced along the way. Yesterday I ran into a snag. I took this part from the thermostat housing /heater core / overflow radiator area and need to replace it. But can not identify what it even is to look into ordering a new one. Can anyone tell me what this piece is called?

 

The closest thing I could find is a heater inlet pipe. The end with the o-ring plugs into the thermostat housing. A heater hose gets connected to the other end. I'm not sure what connects to the extra fitting because the service manual doesn't show or mention it at all. I can't find this part in any GM parts lookups. Is there a part number stamped on it?