When you are replacing a toilet or resetting an existing toilet after a repair, there are a few key things to check to ensure a good seal and prevent leaks. You also want to make sure the toilet sits level and does not rock on the floor, as this can compromise the seal. Toilets are sealed to the floor flange with a wax ring, but the height of the flange and the tightness of the flange bolts (which secure the toilet to the floor) can affect the ring's ability to create a watertight seal.
When preparing to install the toilet, the first thing to confirm is the proper flange height. With the toilet removed, you can see the toilet flange and measure its height above the floor. Optimum flange height to aim for is 1/4 inch above the finished floor. This typically allows for almost any type of wax ring to be used and still ensure a good seal. If you recently tiled or changed the bathroom flooring, the flange height is likely less than optimal.
To get the necessary clearance from the floor, you can add a toilet flange extension, which is quick and easy to install. Flange extensions are commonly sold in 1/4-inch and 1/2-inch sizes to raise the height of the existing flange 1/4 or 1/2 inch. Most extensions come with long bolts, which may be necessary if the flange is below the floor level.
Secure the Closet Bolts
The two closet bolts, which anchor the toilet base to the flange, must first be properly secured to the flange. It is a good idea to use a nut and washer to hold the closet bolts to the flange. This will ensure you do not knock the bolts over when installing the toilet, and it will make it much easier to remove the bolts in the future. When you are buying a toilet or replacement wax ring, check to make sure that it comes with extra nuts and washers, or buy an extra pack while you are at the store (they are sold in inexpensive sets).
Note: If you are using a toilet flange extension, you must bolt the extension to the original flange.
Place the Wax Ring and Toilet
Choose a wax ring of the appropriate size. The type with a polyethylene plastic sleeve, or flange, provides a great seal and fits most standard drains. If the toilet's floor flange height is slightly less than a 1/4 inch above the flooring, you can use an extra-thick wax ring to make up the difference. Do not be tempted to stack up two wax rings because this setup tends to leak. Installing a flange extension or using an extra-thick wax ring will work much better in the long run.
Place the wax ring on the closet flange, not on the toilet. Then, pick up the toilet and set it evenly over the closet flange, making sure the bolts come through the bolt holes in the toilet base. Fine-tune the toilet position, so it's right where you want it, then push it straight down so it smashes the wax evenly. Push until the base of the toilet rests on the floor.
Before you bolt the toilet down, confirm that the base is stable and level by carefully rocking it from side to side and back to front. If it does not sit perfectly flat, it will rock and is more likely to leak over time. To correct this problem, slip toilet shims between the base and the floor to stop the rocking before bolting it down.
The location and the number of shims needed depend on the toilet and the floor; every situation is different. Getting the toilet shimmed before bolting it down will ensure it does not come loose in the future. Once the toilet stops rocking, you can bolt it down with a nut and washer on each closet bolt. Be very careful when tightening these nuts; they should be snug but not overly tight, which can crack the toilet.
Caulk the Base
Cut off any portion of the toilet shims that stick out, and caulk around the base of the toilet with silicone caulk. This will give a little more protection against movement in the future, and it will make the base area easier to clean because you will not get a layer of dust and detritus under the toilet where you can not reach it.
As an option, it's a good idea to leave the back end of the base (out of view) without caulk so that if the toilet leaks at the floor, the water can flow out and alert you to the leak.