Aye Gareth,
OK. I have looked at the SZR660 manual and it would appear that it is the vacuum take-off for the fuel pump, as described on page 126, Section H14, of the manual that I sent you. I cannot remember whether the MZ Skorpion had a fuel pump or not, as I never dived into it's guts that far!
I would suggest that you just blank it off in that case with a rubber cap, if no vacuum fuel pump is fitted.
Hopefully, this solves your dilemma.
My regards, Bill