Many times when someone moves into a new home they notice that they have "slow drains". That is, drains that are not clogged, but do not drain well either.
Most of the time when I see this it is usually in the bathroom sinks and the tub. Why is that? Well, it is gross, but usually you find that the drain on those fixtures is usually clogged with hair. Unfortunately, drain cleaners usually don't break down the hair very well and sometimes makes the clog worse.
Whenever you are moving into a new home, it is usually a good idea (if you are handy) to manually clean the drains out. It is not the most pleasant of jobs, but worth the effort.
Dave Graham, Tempest Home Inspection. Calgary Alberta