Sporadically soap scum will settle in the u-pipe or p-trap.
Having access to Google & Youtube has given several of us a level of freedom that all of us never thought was possible in past years. I’ll never forget the frustration I had trying to learn how to solder electronics back in the late 1990s when neither of these sites existed & your only internet guides were written text & low resolution photos. When I went to Youtube about 10 years later to learn soldering again, I was amazed at how easy the process was once I simply l received the right techniques. That’s applicable to any readily-l received skill as more people flock to sites appreciate Youtube to share their abilities & techniques with the rest of the world. My mother is reading how to use watercolor paints from a series of videos that she started enjoying on a whim one day while trying to kill time waiting on a telehealth appointment iphone call. Although I would call a plumbing maintenance for any extreme plumbing repairs or service, I figured that reading how to flush a hot water furnace would be minimal experience for basic drain cleaning & u-pipe maintenance in my master washroom. Sporadically soap scum will settle in the u-pipe or p-trap. Removing it to clean out the built-up soap scum is much easier than I initially thought. I just had to watch a video on how to re-align the p-trap to get it back into site. You need to make sure you tighten it at the right angle so water doesn’t constantly leak out underneath your sink. Some install water leak detection alarms underneath study room & washroom sinks for this honestly reason.