I have been testing various glues overnight and found a specialized Silicone glue that works perfectly. The material remains flexible yet demands a proper effort to break the bond. Once broken the glue scrapes off without causing any damage to the tube or nipple.
At the moment, I just applied some regular RTV silicone, from the corner hardware store, which I anticipate to be well suited for application by the end user if needed for making a size adjustment. I will wait 24 hours before testing the strength of the bond to be sure.
With respect to the design, we had considered a wire spring clip to secure the tube over the nipple but decided against this as it is too tedious for the user to take off and on without needle nose pliers. A larger more convenient sized clip and the pubic hairs would get entangled with the thin gauge wire.
We decided on the simple silicone ring with its clean lines to maintain the design integrity. I personally have not had the tube detach by itself while wearing the device but we are getting enough reports of this happening to make the necessary adjustment.
I have attached a couple of pics to show the clean finish of the white silicone glue with some red RTV silicone for contrast to demonstrate the precision tolerances of the design and subsequent glue application.
Moving forward, we will be applying the white silicone glue before shipping the product.