Before we go into the actual tip, I would like to mention that this tip would work only for the medium size dents and not the very small ones or very large ones.

The bathroom plunger is a great tool you have to remove the medium sized dents which are most common when you have kids playing around your car. All you have to do is place the plunger and align it to the center of the dent roughly. Push in slowly, and feel the vacuum building up and pull out rapidly. Subtip: don't push in too hard or you may scratch the paint off. You may have to try it out more than once for it to work some times.

The dent should roughly be about the size of the plunger, give or take a few inches.

(AW- Anil)