Place the freshly cut end up against a flat edge, we used a brick clamped perpendicular to the table edge. Leaving about two inches from the cut tube to the edge of the table; again, use that edge to guide your saw. Cut all the way through the tube, creating your first cylinder form.
Prop the forms so they stand up in a bucket, make sure that they will stay upright and fairly level. Slowly and carefully pour in the concrete. You will need to gently stir and agitate the mix in the form as you go to get rid of air bubbles and ensure a smooth finish. Gently scrape across the top of the form to finish and allow the concrete to cure.