Toilet Repairs-Repair that Running Toilet
It's late at night, and you're lying awake, hearing every little creek and noise in the house. Sounds like water running. No one's taking a bath. It 
must be that toilet again. You know the one. The one that is costing you countless dollars of wasted water. This is an easy one for the home plumber. What's leaking, and why? Let's take a look.
There are two major assemblies in the tank. The valve on the left lets the water into the tank, and is usually called a ballcock, or a toilet fill valve. The thing in the center lets the water into the bowl when you flush, and is called a flush valve. The ball cock (fill valve) is usually one of two types. The first type, is usually a brass or plastic assembly with a plastic or copper float ball attached with a long rod (float rod) (4). The second type has a built in float, and is probably made by Fluidmaster, It is usually black and gray. The flush valve is usually like the one pictured ( Douglas type Flush Valve), and is usually made from brass or plastic. Older styles most often have a rubber tank ball (20) attached to the lower lift wire. Newer styles will usually have a flapper instead of the tank ball, lift wires and guide arm (6). Some of the toilets will have a piston like assembly instead of the tank ball/flapper. This type is found on Mansfield and some older American Standard models. Other American Standard models use a hard plastic tilt valve (actuating unit) instead of the flapper. The information below applies to all of these.
Let's fix it! 
First, we need to determine whether we need to repair the ballcock, or the flush valve. This is usually pretty easy. First, remove the tank lid. If you see the water running over the top of the overflow tube (7), then we know that the ballcock is at fault. Pull up on the float rod (4). If the water stops, we will try an adjustment before replacing anything. Flush the toilet, then pull up on the float rod with your left hand near the valve. With your other hand, bend the rod slightly down and let it go. The toilet will continue to fill. If you bent it enough, the water will stop before reaching the top of the overflow tube. If that didn't do it, bend it some more. You want the toilet tank to fill to the lowest level possible and still give a good flush. If this does not stop the water from filling past the overflow tube, then you will need to rebuild the valve or replace it. If you choose to rebuild, you will need the BRAND name and MODEL NUMBER of the valve (not the toilet). Many valves have this information stamped on it. If not, take it to your nearest Hardware Store for the correct parts for your valve. Most repairs only require that you replace the seat washer (26) and piston packing or cup (27).
Problem number two. The water never goes to the top of the overflow tube, or if you have a Fluidmaster type, it sounds like the toilet flushes itself every so many minutes. This is almost always caused by a faulty tank ball/flapper problem. If when you touch the rubber, your hands get black, then the rubber is deteriorated, and needs to be replaced. A lot of tank balls and flappers are standard and fit almost any toilet. The most notable exceptions are American Standard, Briggs, Mansfield, Kohler, Sears/Universal Rundle and Eljer. Take your sample in to your local Hardware Store for the correct replacement.
The actual repair is easy. For the flapper type, unhook the chain from the tank lever (23) and unhook the ears of the flapper from the flush valve. Some flappers are slipped over the overflow tube. Just slide it off and replace. Hook the chain back up so that there is very little play in the chain. You want the flapper to come up as soon as the tank lever if flushed. For the tank ball type, hold the rubber ball and turn the lower lift wire (21) to unscrew. Replace the ball with a new one and replace the lift wires if they are not straight. You can usually replace all of this with a flapper, if you prefer. For Mansfield and American Standard piston types, remove the cap at the top (unscrew) and pull up on the piston. On older models, you will find a washer attached to the bottom of the piston. Carefully pull off and replace. The newer style Mansfield has the washer near the bottom of the tank. After the piston is out, pull off the rubber, which fits inside the groove near the bottom. This is a thin flat washer (looks like a blender washer). American Standard tilt valves (actuating unit) use a snap on or screw on seat disk. Unscrew the disk, or carefully pull off the snap on type and replace.
Problem number three: You have water on the floor. There are two possibilities for this. First, check around the tank to see if the water is dripping down from there. If so, you need to remove the tank. First, turn off the water and flush the toilet. Remove the rest of the water in the tank with a sponge. Unhook the water supply line from the bottom of the ballcock. Next, look under the back of the bowl, where the tank is attached. You will find 2 or 3 nuts or wing nuts. Remove these. If the entire Close Couple bolt (9) assembly turns, you will need someone to hold a long screwdriver in the tank to keep the bolt from turning. At the very least, you should replace the bolt washers and the Close Couple gasket (tank to bowl gasket), which looks like a big black doughnut in the center, between the tank and the bowl. There are different Close Couple gaskets for different toilets. "one size fits 'em all just doesn't make it, especially if you have a Kohler, Eljer, Mansfield, American Standard or Gerber toilet. I would also recommend replacing the entire Close Couple bolt assemblies, not just the rubbers. Check the inside of the tank for the condition of the gasket that seals the flush valve to the inside of the tank. It can be replaced by unscrewing the big nut under the center of the tank. When reinstalling the Close Couple bolts, be careful of how you tighten. Too loose and they leak, too tight and you crack the tank. Go hand tight, and then a few turns of the wrench on each bolt. Hook the water supply back up and turn the valve on. If you get leaks at this point, tighten the bolts a bit until it stops. Go back and forth from bolt to bolt. DO NOT TIGHTEN one all the way and then the other. The tank will crack. This should do it for you.
If there was no leak from the tank, your wax seal (12) under the bowl needs replacing. The safest way to do this is to remove the tank first, although it can be done with the tank on. Modern style toilets have 2 closet bolts (14) that hold the bowl to the closet flange. Remove the nuts from these bolts. If you have a 4 bolt type, also remove the 2 front bolts. Making sure the tank is either off, or the water supply is disconnected, pull the toilet straight up. Set it down on some newspaper or cloth. Clean off the closet flange and inspect for damage. If the flange has sunk below the flooring, you will need a flange extension or a double seal. No big deal. If the flange is above the floor, you will either need to shorten the pipe (difficult) or cut out a piece of plywood in the shape of the bowl to build it up. If it's minor, you can put some Plaster of Paris down and set the bowl in that to build it up. Place your new wax seal around the hole on the bottom of the bowl, and carefully lower over the bolts. New bolts are a good idea.
{TIP} Use an extra nut to hold the bolts firmly to the closet flange. Sit on the bowl to compress the wax and then put the nuts back on the bolts. Sit again and retighten. Do not over do it. Follow the same instructions in tightening these bolts as you did for the Close Couple bolts. The bowl should not rock or move. If it does, try some wedges, or the Plaster of Paris tip above. That should do ya. Your THRONE is ready.