Not sure what they use but...
I don't use poly tube in my plane. We are using Tygothane Polyurethane in our UAV aircraft at work with brass barbed fittings. I used the exact tubing in my plane but used nylon fittings. Much cleaner, simpler, idiot proof and no leaks!
Here is what I ordered from McMaster-Carr
5549K31 CLEAR TYGOTHANE POLYURETHANE TUBING, 1/8" ID, 1/4" OD, 1/16" WALL THICKNESS, 25' LENGTH
FORMULATION: C-210-A
5116K301 FDA WHITE NYLON SINGLE-BARBED TUBE FITTING, ADAPTER FOR 1/8" TUBE ID X 1/8" NPT FEMALE PIPE
5116K81 FDA WHITE NYLON SINGLE-BARBED TUBE FITTING, ADAPTER FOR 1/8" TUBE ID X 1/8" NPT MALE PIPE
5116K13 FDA WHITE NYLON SINGLE-BARBED TUBE FITTING, TEE FOR 1/8" TUBE ID
5116K93 FDA WHITE NYLON SINGLE-BARBED TUBE FITTING, 90 DEG ELBOW FOR 1/8" TUBE ID X 1/8" NPT MALE PIPE