A blocked drain is often very obvious since it would result in water pooling up in a place where it should ideally not be located at all with all things having been considered and taken into account. The thing is that in some cases you might not know that your drain is blocked at all, and as a result of the fact that this is the case you would let the problem get even worse before you think about fixing it in any way, shape or form.
You need to familiarize yourself with some of the signs that could serve as a kind of indication that your drain is blocked in the first place. One such sign that you can use to source, locate and repair blocked drains is to check out how your bathroom smells. If there is a foul smell coming from the drain then chances are that it is blocked so you can call a plumber to make sure that this is what is happening and move forward with a lot more confidence all in all. Paying attention to your senses in particularly smell is a really essential aspect of this sort of thing.
The mistake that most people tend to end up making in this regard has a lot to do with them relying too much on their sense of sight and not nearly enough on their sense of smell. Finding a blocked drain has more to do with smell than sight, and if you wait for visual representations of your drain being blocked then it might just be too late for you to get it fixed at all so use your smell before relying on any other sense.