Plumbers must demonstrate their competence as installers of plumbing systems to an official executing board prior to being issued a license. A plumbing code which is technically perfect is valueless if its provisions are not observed and enforced. The issuance of a license by a community specifies that the holder is qualified both theoretically and practically and that their technical knowledge is sufficient to maintain the standards of the code.

Is licensing intended to prevent anyone but a plumber from doing sanitation work? NO… Licensing prohibits the irresponsible, incapable person from endangering the health of your family, neighbors, and community. Any person may do the work who has sufficient knowledge to do it in a safe manner, so long as the Rules and Regulations of the plumbing and sanitation code are observed. However, those wishing to do such work must demonstrate their ability by taking out a license and passing an examination.

Many states require that, like a doctor, nurse, dentist or pharmacist, anyone whose work affects the public health and safety shall have adequate knowledge and training. No one wants a "quack doctor" to treat his family or a "soda clerk" to fill his prescriptions. For precisely the same reasons, one does not want a "handyman" to do work in his home, office, or factory which can adversely affect the health of his family, his employees, or his neighbors.

Done improperly this work would probably need to be rectified at the time the property changed hands which means paying twice for the same work. Additionally, licensed plumbing professionals are held to a certain standard of accountability – meaning they must perform their work correctly or risk being liable for accidents, damages, illnesses, etc. caused by improperly performed jobs – and must often hold some form of bonding or insurance that can help to protect you in the event of something happening.

So, while that small bathroom remodel might seem like a great, inexpensive DIY project, it is probably wisest to spend a little more and make sure a licensed plumbing contractor performs the work.

This is a big one, and it doesn't necessarily apply to only plumbing. You should never receive a price sight unseen. If a plumber is able to tell you how much something costs before they even look at the problem, I wouldn't trust the price they gave you.

Depending on what kind of plumbing it is, the most effective way to winterize plumbing is to turn the water off, open the plumbing faucet/valve/etc., and use air to blow the water out of the line. If you don't use air, then water will likely get stuck in the line, eventually freezing and bursting during the cold weather. That will invalidate all your work.