T3 2.1 (SS) engine code, 'special sump plug'?

[Gaztop]

I have an ex-German T3 Polizei bus with a 'special sump plug' fixing. The 'sump plug' is a short bolt. and when removed the oil does not come out! The standard plug has been 'upgraded' to a valve. I removed the oil by carefully releasing the valve (behind/above the bolt) with a long screwdriver, the oil ran down the scredriver into a vessel. It appears that this fitting is designed to be used for some automatic oil extraction/evacuation system. It would be usefull to identify the correct fixing to utilise this 'upgrade', I am not necessarily bothered about the complete system, but just the nozzle/fixing that attaches to the sump . Does anyone have experience of this on other buses?

[Aidan]

a picture would really help here as it sounds like "round objects"

[Ian Hulley]

Sounds like the pressure relief valve to me ?