Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

All the tubes I got from Amazon are a bust, the Lowe's ID .170" and OD 1/4" Vinyl with reinforced with Teflon tape is the winner.

What I tried:
1. PTFE Tubing 5mm ID x 6mm OD, complete failure, I more or less expected this.
2. Silicon Tubing 3/16" ID x 5/16" OD, complete failure (as Wayne suggested no more than 1/4 OD and the ID was to big too).
3. Silicone Tubing - 1/8" ID x 1/4" OD, almost worked but it didn't seem to be 1/4 OD (smaller) and the 1/8 ID was way to tight to get on the fitting's nipple or glass.  This might have worked if the ID was a bit larger, perhaps the glass tube would have pushed it out a bit.

So I remade fresh Lowe's tube and wrapped it with some Teflon.  Fully heated up and engine running at the lowest possible speed (stack really bubbling over) zero water/steam from sight glass.  I guess this will be my go to for this size sight glass.  At least it was a under $30 experiment...