A small piece of 3/4" schedule 40 PVC to couple the 13/16 tube pieces together.
We recommend you order and use the larger 1.05" O.D. distributor when possible, which will allow you to use 3/4" PVC pipe for your tube, and not need to order long sections of 13/16" pipe.
Note: The "fit" is very tight when inserting the 13/16" pipe into the center of the 3/4 PVC ( must be Schedule 40 pipe ).
Applying the PVC cement to "glue" them together actually helps to "slide" the smaller pipe into the large pipe.
But do it quickly, as the PVC cement will "set up" in about 30 seconds, and after 10 minutes the two pieces will be permanently connected as one.