When it rains, it pours. I have a very long and jaded history with water. I don't mind lakes and canals, but bodies of water that seem seasonal or are prone to move in unpredictable ways always seem to challenge my need for things to be the same. In terms of my home, I want to know that the course of the water from where it enters my home (water supply) to where it goes down the drain, is reliably boring, always following the same path, guided along by pipes and connections that are water-tight.
My observations and experience with water informed me that the 2nd Law of Thermodynamics applies to my kitchen system: "The Second Law also states that there is a natural tendency of any isolated system to degenerate into a more disordered state." (Wikipedia). That degeneration and resulting disordered state was found in the tail pipe under my kitchen sink, and the remedy was another saga of the DIY variety requiring the infusion of my energy to resolve.
For me, it all begins with data collection, and in the case of the sink, it was a bit of a mystery as to where exactly the water began its escape since the obvious drip was at the lowest point on the pipe - the P-trap plug. Water is always present in the trap and that prevents waste water gases from coming back into the home. Simply wiping the trap clean and observing the water re=appear did show the path of water starting higher up the tail piece So, although the drip was appearing where the plug was, the plug itself was not the source of the dripping.
After wiping down the whole drain system, it seemed that the water was emerging from the top connector where the tailpipe meets the sink strainer body. I thought this metal connector may have become loose over time, so I tried to gently tighten it when the whole pipe came apart under the torque of my wrench. Ah-ha! The 2nd Law of Thermodynamics was right - there was the degeneration in the system.
YouTube is great, though you really need to consult several sources of DIY information to be sure you're getting the right information and not a shortcut from a home owner who meant well, but cut corners or suggested something not quite up to code. It may help to consult the local hardware/plumbing supply people as well.
Once I was certain of all the parts I would need, as well as the tools, I was off to the races with another DIY project. I rehearse the fittings and the sequence of removal and installation just to be sure I understand how it all is supposed to look, and connect. I find my own home's configuration seldom looks exactly like what I see in the books and videos, so this is an important step in order to make sure it all goes the way it is supposed to. For instance, when I disassembled the drain, there was no plumber's putty between the sink cutout and the strainer body, but every video I consulted suggested applying a hand rolled bead of plumber's putty at this junction. So, dutifully, I applied the putty. Everything else went together with little effort.
The result? A no-leak water drainage system! Yay! I"m happy...until my next encounter with, "one thing leads to another..." ;)