Here in the apartment, we often have the problem that the bathtub drain does not work properly. It is not completely clogged, but the water flows slowly and, if nothing is done, drains more and more slowly. We also have to regularly treat it with chemicals or a device that sends a small "compressed air blast" through it. There are still many apartments above us, and we are on the ground floor, maybe that's the reason. I can't think of anything we do ourselves with the bathtub that could cause these problems! I do not regularly pour paint residue into it, nor do I pour cleaning water with mud or stones into it. When we moved in and ran the washing machine for the first time, I found some pine needles in the adjacent bathtub afterwards. In my opinion, the washing machine must have pushed them up there when pumping out; I can't explain it otherwise.
My parents recently had a problem with the drains or the wastewater pipes in their 1970s house as well, but I think the blockage was located elsewhere there, and an inspection hatch would not have helped. My father fixed it again with a spiral in hours of work. If that had not worked, the wall would have had to be opened.