@boskid: That worked, thanks!
I didn't know these worked both ways, I thought the blue arrow was where the tank was supposed to be

Problem solved!

Hi all,
Sorry if this is an often discussed topic, but I've been working on this problem for some time.
If you check the screenshot, the pumps are properly attached to the tank wagons, and the pipes are properly attached to the tanks.
The pipes on the other side of the tanks even show the crude oil ...