In case you want to become a drain leak through apprenticeship, you will have to approach the local plumber's union, who can help you to find a professional plumber willing to hire an apprenticeship.
There are two, one on each side of the toilet, closet bolts which hold the toilet to the floor. If there are caps over the bolts, remove or pop them open. Using a small crescent wrench unscrew the nuts from the bolts. Alternate side to side when unscrewing this will be much more important when reinstalling the water line repair bolts but alternate anyhow.
This so impressed me, that I thought, here is the man who might fix my sink problem, and I told him about my kitchen sink. The look on his face was priceless, as he said, "Ridiculous! Sinks don't leak if they're new." He even showed me what to do. He took out a big heavy-duty screwdriver with a big flat-head blade and showed me. "This is what's probably lose." He put the blade of the screwdriver in a notch the size of a giant screw head that was right in the center of the drain basket where the plug sat in.
A plumber becomes a journeyman once they complete their apprenticeship program and they can apply to be licensed. Most of the plumbers today are in the field of journeyman. To get a license to be a journeyman, you need to pass an exam and pay a licensing fee.
When the drain line stops up it is just a matter of calling an air conditioning contractor to come out and clear the drain line. While he is there he will add an algae preventative to the system to prevent future occurrences. Proper air conditioner maintenance is the key to preventing water line repair leaks.
Turn the water off at the main shutoff valve at the street. You should be able to take a pair of pliers(or your bare hands) and turn the valve at the water meter to shut off the water to your home. Once you have shut off the water you can cut the pipe around the leak and make the repair.
The plumber you hire does not normally do heating but will do hot water heating or in floor heating in the house. Some places you can use the water heater for both domestic hot water and for in floor heating if the heating is a secondary heat. Check with your local plumbing codes on this to be clear.