Yes, you should, if they have done a good job for you. However, a point to consider is that the choice of whether to tip or not is relative depending on the country you live in.
In some countries like Australia, it is expected that all workers must be given a fair pay for their work and in Japan, tipping is not acceptable because working solely for human relations is an upheld custom there.
Plumbers sometimes work in places that are not so clean. That is why if your plumber does a good job for you, it is important to tip him as a token of appreciation.
Tipping is not something mandatory, but if you live in a country where tipping is customary, like in the United States of America, you may need to tip for a job well done.
The main point to consider when tipping a plumber is the quality of work done. A plumber who does shoddy work does not deserve a tip.
Usually, a plumber who has done their work diligently and has offered any extra services like free consultation deserves to be tipped.
How Much Should I Tip a Plumber?
You can tip a plumber any amount you wish, but generally, the tip ranges from 10 dollars to 20 dollars. There is no standard rate, but you can give any amount depending on your generosity, appreciation of the work, financial standing at that time, or any other considerations that you may see fit.