There are other skills plumbers need aside from being able to work with water. One of the most common things that a water leak on is fixing water lines.
If you find that the water line repair leak is in the supply line you will need to replace it or simply tighten it. Start by turning the water supply off and then flushing the toilet to get rid of the excess water. Now use the towels to dry the area so that it is easier for you to fix the leak. Use a wrench to loosen the hexagonal nuts on the supply line at the main end as well as the one which goes to the flush tank. Now use the replacement supply line which you have and tighten the bolt at the supply end first. Now adjust the length that you will need for the pipe to reach the flush tank. Once you adjust the length use a knife to cut the extra length and then tighten the hexagonal bolt at the other end.
The con to time well spent is only if the fix or installation works. Suddenly, when a pipe is squirting water or the dishwasher is leaking all over the floor, that time seems wasted instead of well spent. Now your time is wasted, plus you have to pay for a professional plumber to come over and fix the mess. That time could have been spent doing something else, like golfing or swimming or gardening.
Once you have disconnected the tank remove it from your work space. Do a thorough measurement of the remaining pipe for reference when you go to the hardware store. I will be honest with you, you might need to make a few trips back to the store. Once you get the new tank, slide it into place to line up the plumbing.
Remove the cap of the faucet using slip-joint pliers. Tape the teeth of the pliers to prevent damage of the surface. Remove the faucet cam washer and water line repair the rotating ball.
And the way to know what's sufficient? Well, until the work is done an the bill paid you won't know for certain, but this is the best that can be suggested and normally works very well.
A large plumbing job, such as re-piping or installing additional fixtures, may require a permit. Check with your city's department of building and safety before asking for estimates, and avoid any plumbers who are reluctant to comply with regulations.