The main difference between a p-trap and an s-trap in Plumbing systems is their shape and how they prevent sewer gases from entering the building. A p-trap is shaped like the letter "P" and retains water to create a seal, while an s-trap is shaped like the letter "S" and is prone to siphoning, which can break the seal and allow gases to enter.
You usually have to unmount it and get at the bottom.
The shape of the drain. A P trap drains out the wall. It looks like a P laid on it's side. An S trap drains in the floor. Again if you laid the S on it's side.
Probably rust and minerals that came loose when you turned the water off and plugged the screen in the spout. Unscrew the screen the the end of the spout and see if that doesn't fix it.