A T flip-flop is a fairly complex logic gate, which toggles the output on and off each time it receives a powered input. Sense the button only gives a second or two of current, the T flip-flop allows the button to behave like a switch. If you want, you can read more about them here and here.
Here's the screenshot of what's powering that shower, so you can see how a T flip-flop looks in minecraft.
I am modifying it for looks. One main thing is that it has hot water now (I put two buttons with red and blue wool under them...). I also made it a little bigger in case you have company. Haha, probably not. I might put a chair in too, in case your fat.
I am going to be making a video of my newest creation sooner or later. It is a very large and fancy castle, I named Arroway Castle. Basically, it is a huge castle with lots of furniture. Like the stuff I have put on the original post of this thread. I will post a link when we are done, if anyone is interested.