Trust me, you do not want to wait until you need a plumber to call one! It should be the first call when moving into a new place, seriously. It is imperative to make sure that all pipes are running smoothly and cesspools (if present) are in total working order, because fixing them is enormously expensive.
I recently had a friend buy a nice new home, where everything looked to be totally normal, except for one thing. All of a sudden his pipes stopped working and he had to call a plumber to come take a look at his pipes and diagnose any potential problems. After some inspection, the plumber realized that there was a ton of grease stuck in EVERY pipe. Could you imagine such a dilemma?
Turns out, the previous owners of this house (which had been vacant for 6 months prior to my buddy moving in) had used it as a kitchen to make fried chicken and deliver it to hungry customers, mostly nearby offices. It became a successful business and they were apparently pumping out tons of fried chicken, but obviously this had a very adverse effect on the pipes.
Once they were closed down due to lack of permits, they moved out and attempted to sell. My buddy thought that he was getting a stellar deal, when in fact, he was left liable for a ton of expensive repairs that completely made the initial price of the home obsolete.
Knowing this story is super helpful, because most people will not even consider plumbing because it can not be readily seen when examining a home. That is why it is vital to call a plumber right away!