That is either a short plastic nipple or one of those super cheaper check valves. Look at piece that you have out for small rubber O-ring looking item inside. That would be a check valve. Replace with a brass one.
Whit stuff is most likely pipe dope. Dries up!
You should be able to use an e-z out. I have a sprinkler head e-z out for removing the broken adapters.
Bud
USAF Retired
Pace Arrow
2003 Chev Ice Road Tracker