so i'm experiencing a similar issue. i have the pump to where it's overlapping the tanker as it's in stop, it's on automatic, set to receive the oil, and i've seen the notion that the oil rig needs to not be placed on the direct center to allow pumps to fill the tanker.
so i've done all of that and the tankers still won't fill. I feel like there may be some steps missing that i'm not doing.
oil rig is powered and actively mining, the internal buffer is filling, i have a pump powered by the rig's power so it's marked as working, directly connected to the rig and placed to where its border touches the boat's border (the one that actually receives the oil, not just the edge of the sprite, so yes it absolutely overlaps the tanker) and still, the tanker refuses to receive the fluid. I've looked all up and down this forum for anything else i may have missed and found nothing.