If you find water around the base of the toilet, you probably have a leaking wax seal. This ring seals the connection between your toilet and the pipe in the floor. Before you pull the toilet from the floor, feel the water inlet tube, and see if it's wet. If it is, you have a leak in your inlet, or in the toilet tank. If that's the case, you may not need to pull the toilet from the floor. For the purposes of this discussion, let's assume you've got a bad wax ring.
Before you start, make a trip to the hardware store and buy some parts. You'll need:
- a wax ring - I like the one with the flange on it to help prevent leaks.
- Toilet bolts to hold the toilet to the floor.
- A new water supply line (get the flexible, braided stainless steel type - they're much easier to work with, and less likely to burst).
- A new flush valve assembly.
- A replacement flapper.
- A piece of plastic large enough to sit the toilet on while you're getting it ready to reinstall.
If you have a cleaner in your tank, remove it and run clean water through it until you get rid of all the residue, then shut off the water to the toilet, and hold the flush lever down until all (or most) of the water drains out of the tank. You'll still have a little water in the tank and the toilet bowl. If you want to avoid a mess, pump the water out of the tank and the bowl (a wet/dry shop vac works good for this, or you can use a small hand pump). Loosen the connection on both ends of the water supply line, and remove it.
The toilet is attached to the floor by two bolts through the base. They're usually hidden by a plastic cap the matches the toilet. Pull the caps off (save them), and turn the nuts counter-clockwise to loosen them. At this point, you can gently tip the toilet slightly, lift it off the bolts, and set it on the plastic. Assuming the water is drained from it, you can carefully lay it on its back to gain access to the bottom.
Take a putty knife, and clean off any residue from the old wax ring from the pipe flange in the floor. The bolts slide into slots in the floor ring, remove and discard them. When the flange is cleaned up, seal it temporarily with a piece of plastic until you're ready to put the toilet back on (this will keep sewer gas from filling your house).
Go back to the toilet, and clean off the bottom where the wax ring goes. As long as you've got it removed, go ahead and replace the flush valve and flapper. The flush valve is the part that controls the water coming into the tank. Remove the nut on the bottom of the tank where the water supply line comes in, and lift the valve out of the tank. The new one will install with the gaskets/washer included (some of these are different than others, follow directions in the package). In any case, snug the nut up firmly, but not so tight that you strip the plastic threads. The flapper valve either slips over the overflow tube, or attaches to little tabs on the tube, depending on your design. There are many universal replacement flappers that work with either style. Clean the seat for the flapper with a bit of steel wool or a clean rag, so it makes a good seal. Hook the chain from the flapper to the flush handle.
Lay the toilet on its back, and take your wax ring from the box. Important: if your bathroom has been tiled, the floor flange may be below the surface of the floor. If this is the case, you'll need an oversize wax ring, to make a proper seal. If this is the case, run to the hardware store and get one. Don't use an oversize ring if you don't need it.
Remove the plastic from the floor pipe, and insert the bolts in the slots with the threads facing up. Take the wax ring, and place it on the pipe, with the rubber flange inserted into the pipe. Get a helper, if needed, and pick the toilet up. Gently set the toilet onto the ring, being careful to go directly down onto the ring, You may find it easier to put the ring on the toilet, instead of on the floor - either way will work - the important thing is to make sure you get everything lined up properly before you set the toilet down.
With the toilet in place, put your weight on it, and rock it slightly to push the toilet down so it sits flat on the floor. If it won't get close to the floor, you either have too high a wax ring (only if you've gotten the thicker one from the hardware store), or you're not lined up properly. Wiggle it a little, and see if it drops down - if it is really solid, you have something not right, and you'll need to try again.
Most of the time, the toilet will be close to flush with the floor, and will go down with a little pressure. Once you've got it seated, put the washers and nuts on the bolts, and tighten them hand tight. Important: you must tighten the bolts evenly, and you can't put too much pressure on them. If the toilet won't seat completely on the floor, don't try to force it with the bolts (you'll break the toilet). If necessary, let it sit for a day or so - it will probably seat itself eventually. If you do this, tighten the bolts a little bit a couple of times a day - you'll probably find that they will be loose when you come back to check them. Eventually, you want the bolts to be snug (more than hand tight, but not super tight), and the toilet to be sitting completely on the floor. Install the little plastic caps over the bolts.
When you have this done, connect the new water supply line, and tighten securely. You're ready to test and adjust the system!
Turn the water on slowly, and watch for leaks. In particular, check the gasket where the flush control valve is mounted. Adjust the water level so that it is below the overflow tube, and even with the "Fill" line. Flush the toilet, check for leaks, and adjust the flapper or flush valve as needed.
If you have a leak at the water supply line or flush control valve, you can usually fix that by tightening the appropriate nut a little. Don't overdue it!
If the toilet leaks around the base, you've got the wax ring installed incorrectly, and you'll need to pull it apart and start over (with a new ring). If you're careful when you install it, this is highly unlikely. When using the ring with the flange, I've NEVER had one leak when I installed it.
All this may seem like a lot of trouble, but it's really a basic do-it-yourself job. All the parts you buy will have instructions with them, and you'll follow the exact same process if you decide to install a new toilet. Just relax, take your time, and everything will work just fine.