dont think it's allen wrench.
i just tried to adjust mine. seemed to be pentagon shaped instead of hex.
will try take a picture.

Problem is, who can we contact to get it adjusted the properly?

ozak any idea what size is it?
i need to take picture, but mine is installed upside down so bit hard.

ball valve needs to be before the non return valve.
can close to change out the non return valve if required.

bypass the pump also can use the same concept. need non return valve.
else the pump discharge will pump back into the pump suction.
waste energy.

should consider to change to ABS pipe then.
seen the manufacturer did pressure test on the pipe after 5 minute of joining