Measure the inner diameter of each tube, choose how tight each end should seat, and get a printable tapered adapter that bridges them. Deterministic and free.
Join two tubes of different sizes. A tapered adapter whose ends dial from snug to loose to slip over each hose.
Inner diameter of the wide end. The Fit slider adds clearance on top.
Inner diameter of the narrow end. The Fit slider adds clearance on top.
How thick the tube wall is. Thicker is stronger but heavier.
How loose the printed part sits on the thing it mates with. Looser prints fit more easily.
Snug adds 0.10mm, Normal adds 0.25mm, Loose adds 0.50mm to the surface that mates with your object, so the printed part clears it without extra sanding.