In the Philippines, we discard used toilet paper in the trash can in the toilet. I heard that it is difficult to dissolve the toilet paper in water, and the piping of the sewage tends to be clogged.
In Japan, we discard used toilet paper into toilet bowl. Since toilet paper made in Japan quickly dissolves in water, piping will not clog unless you flush to a large amount at once. Therefore, we do not need to dispose of it as garbage.
By the way the airline toilet is the same as in Japan. We can throw the toilet paper inside the toilet.