So you have a male and female connector with no threads?.......maybe some kind of quick connect? A picture might help. If I understand your description ....cutting off the female connector on the 4” hose as suggested would work to get your antifreeze into the pump/system......but then you have to seal the now open Winterizing hose end (assuming a simple system is what you have). A barb hose fitting to 1/2” male adapter with a matching plastic threaded cap would work to seal your winterizing hose when you are done.
I was going to suggest something like the link below......but if you go to any local RV Dealer you should be able to find fittings that will resolve your issue. In Alberta, Fraser Way used to have various 1/2” RV plumbing fittings in parts drawers for retail customers to pick through as an example.
https://www.etrailer.com/RV-Fresh-Wa...rra/RF841.html
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