A few weeks ago I installed a new fill valve into the toilet and we thought that would fix the " constant running" problem we had. Well, it didn't fix shit and I was forced once again to go toe-to-toe with this waste-eating beast. Instead of constantly flushing, the problem was enhanced by the new fill valve. Now every hour or so it would sound like the toilet is magically flushing itself.
This went on for a few weeks and then on Monday morning after my shower I was standing in the quiet bathroom and I heard the clue that would unravel this mystery. This was a dripping sound coming from the toilet. I checked around the toilet to make sure nothing was dripping on the floor. There were no drips. At this point I figured there had to be a leak somewhere between the tank and the toilet itself. After talking with some co-workers and researching how a toilet works on the internet I figured that the flush valve had to be leaking somehow. I would have been able to confirm this had I some food coloring which I could have used to color the water in the tank and watch to see if it leaked into the bowl. I did not have food coloring so I didn't get to try my cool experiment.
Saturday rolls around and we head out to buy a flush valve. I had no idea what I was buying but what I found is that this is quite a universal thing so there were no options, just an entire shelf of the same exact valve. We got home and I started in at 10:30 AM. The instructions said to drain and remove the tank. I shut off the water, drained the tank as best as I could, unhooked the hose that fills the tank. These were all the same steps as last time so I used my memory of the watery mess I made and placed a water catching device (cool whip container) on the floor to catch the water. All of the water fell into the container and not onto the floor (yay). Then I knocked the container over and the water went all over the floor (shit). Now that the floor was considerably wet I had to remove the tank from the toilet. The tank at this point has a little bit of water at the bottom and is filled with the sediment from years of well water sitting in it (it looks like a brown sludge). I unscrewed the tank (and got more water on the floor) and lifted it off of the toilet. I then ran the dripping tank outside so I could clean it out with the garden hose.
What I found at the bottom of the tank proved my theory that the flush valve was leaking...

-The rotted gasket
The gasket that sat underneath the tank where it met the toilet crumbled in my hand.
I cleaned out the sludge from the tank and also cleaned off the back of the tank which had built up a nice dusty icky coating then I brought it back inside. The next step according to the supplied instructions was to remove the old flush valve, easy enough. What they failed to mention is that the big plastic nut that holds the flush valve in place is gigantic and far larger than any wrench I have ever seen. I tried the biggest wrench I had and it wasn't even close. I tried to remove it by hand and with a jar opener and it did nothing but stared back at me in defiance. Out of desperation I tried to fabricate a device to remove it using wood which like the all other attempts resulted in failure. Now that I'm pissed and swearing like a sailor I grabbed a pair of pliers and started breaking off pieces of the valve so I could pry the nut off. Now I have a pile of broken plastic and a flush valve that is still in place. I then grabbed the top of the valve from inside the toilet and pulled on it until it snapped, sent the bug nut flying across the bathroom and my arm scraped from bashing it into the side of the tank. The bitch was out.

-The remains of the stubborn flush valve.
Putting the new valve in was quite easy, I just had to trim a bit off the top of the tube so it would fit in the tank without a problem. I put it in place and HAND TIGHTENED (per the instructions) the new big plastic nut in case I have to remove it again. Then I hooked the chain up to the flush lever to make sure it would fit ok and it was perfect. The only thing left to do was hook the tank back to the toilet (sounds easy eh).
The old bolts (and rubber washers) that held the tank on were all corroded so they needed to be replaced by the nice new ones in the supplied kit. Well this is where everything went south. The new bolts were exactly the same size as the holes in the bottom of the tank. This means they did not want to fit without a fight. One went in without a problem, the second one was a freakin' disaster. It had no intention of ever going in that hole without a fight. I ended up developing a method of putting this second bolt in by putting a piece of wood (from the failed tool construction earlier) on top of the bolt and then hammering the wood with the end of the pliers I had. This worked great until the big rubber washer on the bolt couldn't get by the newly installed flush valve. I tried to wiggle it and get it around the valve but it was not happening. This led me to take the goddamn valve out again (good thing I hand tightened) hammer the bolt in the hole, and put the valve back in.
I placed the tank back on the toilet and put a nut on the end of one side (screwed right on using only my hand) then I went to put the nut on the other side and it wouldn't go on. I managed to screw the threads up so bad trying to get the bolt in the hole that it now required me to use a wrench to get the nut on. I got it about halfway on then realized that I screwed up the washer placement on the bolts AND HAD TO TAKE IT APART AGAIN.
After proper placement of the washers and nuts I put the tank back on and fastened it using the supplied wing nuts. It was at this point I hooked everything up, turned the water back on, adjusted a few things and had a flushing (non-leaking) toilet.

-The flushing (non-leaking) toilet.
Oh yeah it was now 12:30. That was 2 hours of pure unfiltered misery that I suffered through but it was worth it because our toilet has not randomly flushed, made a dripping sound, or leaked in the last day. I hopefully have defeated this monster.