Bosch GBL 18V-120 (Affiliate link) Adapters for inflatable things.
The adapter overall is 70mm long, the upper cone part is 20mm long.
I recommend to print it with TPU, but PLA and so on will also work.
There is also a deflation/suction adapter in my uploads.
Print Profil Build Plate selection:
see also my other models eg
Bosch GBL 18V-120 deflation adapter