I use PVC in pretty much everything aquarium related.
Its a cheap life hack for stacking rock easier, it makes great hidey spots and burrows for certain animals that are hard to construct them out of rock for, and its for the most part what we use for the plumbing because what else attaches to overflow bulkheads.
For burrows I often go the extra mile and use a nail filer/sandpaper on the inside, just to make it less smooth for little shrimp and crab feet to attach on easier, otherwise some of them can't climb or hang off it.
The only thing I've always wondered about PVC is the ink they use to write on it. Usually its bar coded and labeled directly on the pipe and for years I always sandpapered that off just out of paranoia of something leeching from it.
ABS AFAIK is basically the same thing just some different capabilities, I've always just called it 'black PVC' which is less noticable inside the aquarium, I don't think it matters in hindsight bar aesthetics for aquariums, just one is more expensive.
