I'm not so sure. A lot of trash plastic degrades over long periods of time. They might find the plumbing (which is a type of plastic that lasts longer), but that isn't trash in general.
I don't know. A lot depends on how they are. UV is the main degrader of plastics in general (but I'm not sure about PVC in particular), but in walls or the ground that isn't a problem. PVC is often used for vent pipes where it is allowed through the roof with no treatment - but failures in this application are not a disaster (no pressure). HDEP (black water pipe - not to be confused with ABS which is sometimes used for drains) pipe has a history of 50 years in the ground with no sign of failure. PEX is expected to last 100 years in a building, but in one month of sun exposure is enough to make it no longer able to hold water pressure.
I've named 3 types of plastic, you can't apply a blanket statement about any of them that applies to the rest.
I read someware that in 2000 years the books we managed to save from the middle ages and up to about 1850 will still be around but anything printed after that will be gone because the paper of the modern age is to fragile to last.
The cultures that dominated North and South America prior to the arrival of European explorers and the mass plague that accompanied them were absolutely vast, and we are only now starting to piece together the size and scale of some of those empires.
There are several reasons for the gap in understanding of their scale, but one is that the well-settled communities (with some exceptions primarily centered in South America) often used primarily wooden construction, as wood was extremely plentiful in the New World. When the European plagues led to 90%-plus die-offs in these cultures, the survivors couldn't maintain the scale of cities they'd built, and since wood rots relatively quickly, their permanent settlements were all but eradicated by the time any subsequent waves of European exploration arrived to write down what they saw in languages Europeans could read.
Modern archaeology techniques, by analyzing land cultivation and the few remnants a wooden building leaves of foundation, are starting to comprehend the scale of the cities built by the original settlers of North and South America.
They were also about as complex and technologically advanced as their Old World counterparts. I'm consistently impressed by how well South American cultures understood the cosmos, plumbing, irrigation, materials, etc... South American civilizations would have been a source of new information, and no doubt a bunch of knowledge was lost.
We only have a few books left from thousands of years of civilizations. It makes me incredibly sad to think about the history we lost. It would be like if we only had one or two books to understand all of Roman history. Absolutely blows my mind how fragile everything we've built is.
