I was asking similar questions a couple weeks ago and got some good answers:
http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/672927-what-look-vacuum-pump-c.html
It's not good to use shop air to pressure test or flush the system because of the moisture in it. What I found is that unless there's been a catastrophic failure (the compressor blew up) it's not usually necessary to flush.
The low port on your car is located kinda on the top of the compressor. To get at it, you really need a 90 degree elbow fitting like this:
https://www.ackits.com/pc/35-50003/conversionitems/35-50003+-+Low+Side+Conversion+Fitting+%2890+Degree%29