I have an EHEIM 1262 I plan to connect as an external pump with PVC. The in/out conections are hose barbs with a strange threaded collar :? below the barb. The barb fitting can be removed to expose a 3/4" thread, but a MPT PVC adapter seems to bottom out before the threads are tight?

Has anyone connected one of these pumps externally? Am I missing an "Optional" part (adapter) from EHEIM?

Thx - Steve