I got this VEVOR first start up was impressive, Smith it off an hour later 50% flow ...the more I turn it off the weaker its become.. I have ordered another to see if its a LEMON will let you know in a weeks time. (10Jan,23)
We all have the same connection problem to the metric pump connector. I bought a 1-1/2" Insert Fitting from Lowes part # 474-015 (?)which has those barbed outside threads. I filed those threads to make it smooth and was able to push fit that (no glue needed) into the metric pump connector and is leak proof. Of course then a regular 1-1/2 " pvc pipe would connect to this Lowes part. Picture would help to make sense here but I cannot attach it here.
Got same pump for my pond from Amazon, but the brand I got is called "Landshark". The hose connectors on them are "2 inch" hose connector but normal 2 inch pvc are too big and threaded pvc are too small. It has been frustrating dealing with different PVC pipes, their listed sizes are not universal.
I had to make some ideas to make the connection right as you explained. I just hooked it up after all connection innovations and it gets little next to no suction. any thought?