[Tookie]

You need to use an extractor bit to remove the remnants of the valve. If you damage the threads while doing so you may have to re-tap the receiving end of the assembly; or failing that, using a short hex bolt to plug the remaining hole may work best. A rubber heat resistant washer/gasket under the bolt should seal any potential leaks. As a last resort, seal the outlet and drain through the hose when needed.