[jdmccright]

The original fittings were made from zinc, and end up corroding badly...two of them, one in front and one in back to serve the heater core. Dorman makes steel replacements if you want to stay OEM pipe connections...test them with a magnet to be sure they are steel. Others will find a plain hose fitting adapter, screw it into the manifold, cut the quick-connect ends of the hoses off, and band-clamp them. Either way works.

I would be careful hammering at the piece remaining because any big pieces that break off go into the manifold and may not get flushed out. As suggested, you can saw part way into the piece through the hole in two opposite places. Then tap a screwdriver at the midpoint between the cuts to make it collapse on itself. Once you get it out, flush it thouroughly with water to get rid of the shavings.

Good luck!