Installing a new Pieburg vacuum pump. Instructions say to install pump, leave both vacuum lines disconnected, start the car and feed a bit of oil into the nipple where the brake booster vacuum hose connects to the top of the pump.

I’m not very familiar with the vacuum system but it seems wrong to me to introduce oil into the vacuum port of the pump, wouldn’t it just suck oil into the brake booster?

Vacuum is the absence of pressure/atmosphere. The atmospheric pressure of about 14.5 psi moves into the vacuum/low presser (higher pressure goes to the lower pressure) created by the vacuum pump and is exhausted into the engine.

If I was to call it a flow the flow is towards the vacuum pump.

__________________
84 300D, 82 Volvo 244Gl Diesel