It is located at that hole and goes in from the bottom. From there up the water tube is cast in. When the tube and grommet are removed, the hole continues into the exhaust cavity. The grommet has projections on the sides to lock it into the housing. The installation tool can be made from a threaded rod of a diameter that will easily fit into the grommet is fitted with a nut and washer to push the grommet in place. It is ground away on opposite sides so the locking projections on the grommet have room to retract. The also enables you to twist the grommet. Coating the grommet with KY jelly makes it easier the slip into place. It is twisted back and forth to get the projections in place. Hopefully when the one you see on the outside is in place, the one you can’t see will be in place also. Be sure there are no rough edges on the water tube. The KY should make it easy to insert the water tube. . . 😉
