Ah, but here’s some good news. This is really exciting! The Amico 5/8″ OD 2M Black Soft Corrugated Tube Cable Pipe Bellows Hose I showed earlier fits very snugly into the 5/8″ ID Proline. (I think, by the way, that the Proline is not as good quality as the same dimensions tubing sold by the foot at Lowes/Home Depot or Ace.) The further the Amico is slid (slided?) up into the vinyl tubing, the more secure the connection.