It’s just the
cheap clear pvc tubing. Most likely a little kinked from the factory no less. I don’t know the diameter, probably about 1.5”, but not sure.
Why do you need to replace it? Leaking? Mine was, but it wasn’t a hole in the hose, it was a bad seal with one of the fittings. You probably want to do a little spelunking either way to investigate before you start
buying things. I find ear muffs and a shop vac make life a little less miserable under there, you can vacuum up all the dust and loose EPS beads as you go so they don’t end up stuck to you.