In the picture, those are 3 inch round by 1" think bars. The bottom of the tube had one of these: https://www.amazon.com/EVERCONNECT-1730-Flexible-Stainless-Clamps/dp/B00HNWADI2

Tape doesn't stick to parchment, it only needs to hold when pouring, once poured the weight of soap mixture will hold it in place. In the attached pi, red is the tube, green in the parchment and arrow it where to tape it. . We found plastic tube bags from a commercial supplier to be significantly easier and faster.