Step 6: Rotating pipe joint / swivel fitting
This part is still a work-in-progress for us.
At the moment, we have a 6" length of pvc pipe that fits snugly into the pvc connector, and - lubricated with automotive grease - this can be held in place by hand and works reasonably well. We also cut off this pvc adapter and used just the plain blue hose fed into the bottle outlet as it was an excellent fit and gave more working room.
The rotating joint is perhaps the most important part of the pump. When we've chosen the best of our designs, we will update this step with the details.