No worries about loosing the oil,just solder a 1/4" male flare fitting on the suction tube and carefully bend the other so it is pointing up at least as high as the top of the unit and fasten some cloth over the open end.I have used one of these for several years on both R-12 & 134 systems on my cars and the engine driven freezer/fridge on my boat.It will pull a vacuum as far down as my gauges go,plenty good enough for any small systems.While you are at it check out this,a friend of mine is a HVAC expert looked it over and says it looks great to him,he is is going to switch my MB to this stuff.
http://autorefrigerants.com/co00033.htm Don