The best way to replace the old side tube is to take the nylon tip off the old silicone tube, pull out the internal wire, cut the old silicone tube about 1/2" above the top of the aluminum tube that sticks out the front of the QuadStick and then insert the brass tube into the old silicone tube. (Discard the 1" long silicone piece that may be on the bottom end of the new brass tube)
If you would like to completely remove the old silicone tube and replace it, do not attempt to pull it off. We had a instance where simply pulling the old tube broke the aluminum tube off the pressure sensor. This video demonstrates how to cut off the old silicone tube and install the new side tube assembly. DO NOT apply sideways force to the aluminum tube when attaching the new silicone tube..
Replacement silicone tubing can be ordered from Amazon.