Fill port on rifle looks like :-
although it may or may not have the 'T' shaped piece on the end. The bit on the filling hose end (filling adaptor) looks like:-
If you have the 'T' on the end as the first picture it goes through a matching slot in the adaptor (not visible in the second picture). If you don't have the 'T' piece on the rifle then either of the two types (slotted or unslotted) of adaptor will work.
You might want to upload a picture of your setup in case you mean something entirely different.
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