Best ways to sterilize plastic and metal?

So, I was wondering how you guys would go about actually sterilizing (not just disinfecting) plastic and copper tubing? It’s for a custom water-cooled PC loop, and I’d much rather stick to distilled water instead of using some antifreeze stuff. My main goal is just making sure nothing starts growing in there, since those little microbes absolutely love it when things sit around at 70 ˚F. Any ideas? And uh, just a heads up—the pump definitely can't handle 400 ˚F.

So, you looking at one-time sterilization or what? Like, are these pipes even going into a sterile environment later on?

You can hit them with UV light if you aren't using heat.

I mean, you'd probably just have distilled water running through those pipes, maybe some mineral oils or whatever chemicals they use... though I doubt anything in there could actually support life, especially since it's pitch black.