Plastic Tubing Diameter For Brake Bleed.

Probably 5 or 8 mm will do it.

 

I use tubing from a fish tank
Available from pet shops or from a friend that keeps fish
I got mine from a garden centre...about a foot and a half and they just gave it to me
It’s clear so you can see the air being expelled and soft enough to fit most bleed nipples

 

I usually use clear plastic tube with a short piece of rubber tube to fit over the bleed nipple with a bolt in the other end as a blank / weight and put a cut in the side at the bolt end to create a one way valve ( one person bleeder ).

The rubber is usually easier to fit to the nipple as its softer and is a good enough fit on the plastic tube

 

Fit the pipe or pipes (twin disc) and fix straight up at speedo height then fix to a syringe undo the nipple and suck the fluid though