Ask around. Ask your friends, ask your neighbors and get referrals. Nothing is more powerful than the testament of someone who has had a local plumber in their home and can speak to his/her capabilities.
If you need an emergency drain repair, toilet repair, or some other plumbing job completed you'd be better off to go online and find a proper business. The best businesses are almost always ranked towards the top because Google is so accurate with their searching relevancy. So if you type in your city and the word plumber you will be given the best in your area!
Second, do you have the knowledge required to solve leaking pipes/faucets and clogged drain problems? You should be able to understand the parts of the faucet, pipes, and drain. Various types of faucets are sometimes designed to function very differently. You should know how to dissemble it replace the busted part and drain line repair put it back together again. If the problem is in the pipes, you should know which one you have to remove and replace.
A good company offers guarantees on their labor and the parts they use. Reliable plumbing companies guarantee their work Trustworthy plumber with written warranties and contractual agreements. If you pay for service and it fails, you will not have to pay for the same service again if the work is guaranteed.
Your septic tank has to be emptied sometimes, and there's no easy answer to when it should be done. It depends on the size of the tank and the (sorry to mention it) consistency of the stuff going into it. Basically, if the septic tank isn't pumped out regularly, it will cause you thousands of dollars worth of problems. Ask your Local plumber for advice on your septic tank maintenance.
The nest best bet is the yellow ages. You can look up the yellow pages. The yellow pages will have information regarding every service agency you require. You can try to look up the internet for a little additional information. The internet is also as well detailed and is updated more e often. There are plenty of plumbers advertising themselves on the internet. You can also find these advertisements in news papers.
Most importantly, make sure that you set your foot in a reliable and trustworthy store which also offers great discounts or sales for you to be able to save.