I know that some people say that PVC is fine for racking tubes, but I have someone who is looking for an alternative--HDPE or PP would be acceptable but not preferred. Since PVC is the only type of plastic tube our local hardware store sells, are there some DIY alternatives that have worked well for people? (Caoutchouc? Sheep's intestine? What'd we use for this before plastic came along?)
If vinyl isn’t the gold standard for homebrewer’s tubing, I don’t know what is. It’s good to ~170° F max.
As Tobias mentioned, silicone tubing is used for higher temp transfers.
Purchase anything anywhere “Food Grade” and you’re good-to-go for low-temp homebrew, but I wouldn’t get too creative with random hardware store DIY bric-a-brac without the “Food Grade” claim. There are some hearty anti-fungal additives to many compounds. (Case in point – when sinking a ball valve into a mash tun, make sure and purchase your silicone sealant from your local tropical fish store vs. the first thing you see at Home Depot.)