The problem with tiny pipes (i.e., any pipes with diameters less than 3/4") is that leaks, holes, and flaws are even tinier and harder to see. However, a plumber or plumbing inspector can find these tiny flaws with the use of pipe cameras. Here is how they do it and what you can do about the tiny flaws they find after the fact.
Slinky Snake Camera
The plumber uses a snakelike hose device connected on one end to a case and a small video screen. On the other end of this articulating hose is a light and a tiny camera head. The plumber inserts the lighted camera end into a small diameter pipe. They continue to feed the camera into the pipe manually, pausing each inch to rotate the camera and look for flaws in the pipe. The LED light on the end of the hose near the camera lights up the pipe fully so that the plumber and you can both see the entire internal expanse of the pipe. By rotating the camera every inch and doing it very slowly, the plumber can spot places in the pipe that are leaking, damaged, have a hole, and/or are about to break loose. They will take pictures of these areas and make notes about where these areas are in the pipes.
What to Do with the Findings
You could stand near the plumber the entire time that they are winding the lighted camera through the pipe, but many wait until the plumber is finished. Then the plumber will share their findings with you, using the snapshots and/or recorded video to show you what is going on inside these smaller pipes. Then you have a few options as to what you will do with these findings and what to do with the flaws in the pipes.
Replace the Pipes or Seal the Holes
Most homeowners, after viewing what is wrong with their small pipes, choose to replace the pipes. Sometimes they can upgrade to a slightly larger pipe diameter, which will help them find any issues with those pipes in the future. The rest of the homeowners opt to seal the flaws and holes in the pipes. To do that, the plumber drains the water from the pipes and closes water flow off from the pipes that need to be sealed. A clear plumber's caulk closes the holes and leaks, and then your pipes will work well again.