Every through-hull fitting in your boat is a potential hole that could sink you in a matter of minutes. Although they are out of sight and, at times, difficult to get at, through-hulls need careful routine checking, at minimum every three months. Many through-hulls such as engine-cooling intakes and sink or cockpit drains, tend to be left open continuously and the valves may stick in the open position. You should operate the valve by turning it on and off to make sure that when an attached hose fails you can stop the water flow.
As an additional precaution you should get wooden bungs (tapered soft wooden plugs) for each through-hull in your boat. (You can get them at most Marine Supply stores.) Make sure that they are the proper diameter to fit in the through-hull. Once you get them back to your boat, don’t just throw them in a drawer. Take each appropriate size to the through-hull it fits, drill a hole in the larger end and thread a string or monofilament line through and tie it to the through-hull fitting. When the inevitable happens you won’t have to go looking for the bung. Just reach down, put the tapered end in the hole, and press down until tight and the leak has stopped.
Remember, a two inch hole just a few feet below the waterline can sink a 30’ boat in just a few minutes.