Vacuum Port Cover

[mechar]

The vacuum line on my in-ground gunite pool currently has a slip fitting. I would like to put a spring loaded port cover on the port, but it looks like they are only available for threaded ports. Is there a cover available for slip fittings, or a way to replace the current slip fitting with a threaded one?

 

[dtlight]

Presumably you could ream out the existing hole and then tap threads into it for the threaded port cover, but if anything goes south you could end up with a mess that's not easily repaired.