What You Need to Do Before You Start

Installing a replacement toilet is a project most homeowners can complete in two to three hours with basic tools and no plumbing experience. The process involves shutting off the water, removing the old toilet, preparing the floor, and securing the new one in place. You will not need to cut pipes or solder anything—modern toilets connect to existing supply lines and drain openings that are already in your wall or floor.

Before you buy a new toilet, measure the distance from the wall behind the toilet to the center of the drain hole in the floor. This measurement, called the rough-in distance, is almost always 12 inches in North American homes, but some older or renovated bathrooms use 10 or 14 inches. Buying the wrong size means the toilet will not fit properly or will sit too far from the wall. Check your current toilet's documentation or measure it yourself to be certain.

Gather your tools and materials in one place before you begin: an adjustable wrench, a flathead screwdriver, a putty knife, a bucket, towels, a wax ring (comes with most new toilets), shims, and caulk. Turn off the water supply valve behind the toilet by turning the handle clockwise until it stops. If the valve does not work or does not exist, turn off the main water supply to your house.

Key Takeaways

  • Measure the rough-in distance (wall to drain center) before buying a new toilet, as 12 inches is standard but 10 and 14 inches also exist.
  • Turn off the water supply, flush to empty the tank, and disconnect the supply line before removing the old toilet.
  • The wax ring seals the connection between the toilet and the drain—it comes with most new toilets and must be pressed onto the drain opening before the toilet is set in place.
  • Shims under the toilet base keep it level and stable; caulk around the base prevents water from seeping underneath.
  • Do not turn the water back on until the tank is fully assembled and all bolts are hand-tight.

Removing the Old Toilet

Flush the toilet to empty the tank as much as possible. Use a sponge or towel to soak up any remaining water in the bowl and tank, then squeeze it into a bucket. This step prevents water from spilling across your floor when you disconnect the supply line and remove the toilet.

Locate the water supply line—a flexible hose or rigid pipe connected to the bottom left of the tank. Use an adjustable wrench to loosen the nut where the supply line meets the tank. Turn counterclockwise until the connection is loose enough to unscrew by hand. If the connection is stuck, explore penetrating oil and wait 10 minutes before trying again. Once disconnected, let any remaining water drain into your bucket.

Look under the toilet base for two bolts on either side, usually covered by plastic caps. Pry off the caps with a flathead screwdriver. Use your wrench to loosen the nuts on these bolts, turning counterclockwise. Once the nuts are loose, you can usually unscrew them by hand. If a bolt spins without loosening, hold the bolt head steady with a second wrench while you turn the nut.

Rock the toilet gently side to side to break the seal between the wax ring and the drain opening. Lift the toilet straight up and set it on its side on a towel or cardboard. The old wax ring will stick to either the toilet or the drain opening—scrape it off completely with a putty knife. Inspect the drain opening for cracks or damage; if you see any, contact a plumber before proceeding.

Preparing the Drain Opening and Installing the Wax Ring

Clean the drain opening thoroughly with a damp cloth to remove any remaining wax, debris, or mineral deposits. The surface should be smooth and dry. If the opening is recessed or uneven, you may need a wax ring extender (a thicker wax ring) to may support a proper seal—your new toilet's documentation will tell you if this is necessary.

Press the wax ring firmly onto the drain opening, centering it so it surrounds the opening completely. The wax ring is sticky and will stay in place. Do not remove it from the drain opening until you are ready to set the toilet down, as it will lose its seal if disturbed. If you accidentally dislodge it, remove it, clean the opening again, and press a fresh wax ring in place.

Check that the floor around the drain opening is level using a spirit level. If the floor slopes or has low spots, you will need shims to keep the toilet stable. Shims are thin plastic or wood wedges that slip under the toilet base. Have them ready before you set the toilet down.

Setting the New Toilet in Place

Carefully lower the new toilet straight down onto the wax ring, aligning the bolt holes in the base with the bolts sticking up from the floor. Do not slide or rock the toilet—lower it straight down to avoid disturbing the wax ring seal. Once the toilet is resting on the wax ring, you should feel resistance as the wax compresses.

Insert the bolts through the holes in the toilet base and hand-tighten the nuts. Do not use a wrench yet. Check that the toilet is level from front to back and side to side using a spirit level. If it rocks or tilts, lift the toilet slightly and insert shims under the base where needed. Shims go under the front corners or sides, never under the center. Once the toilet is level, tighten the bolts with your wrench, alternating between left and right to keep pressure even. Tighten until snug—do not over-tighten, as this can crack the porcelain base.

Snap the plastic caps back onto the bolt heads to cover them. If the caps do not fit because the bolts are too long, you can trim the excess bolt with a hacksaw or have a hardware store cut them for you.

Connecting the Water Supply and Testing

Reconnect the water supply line to the bottom of the tank, hand-tightening the nut first. Use your wrench to tighten it another quarter turn—snug but not forcefully tight. Turn the water supply valve on by rotating the handle counterclockwise. Water will flow into the tank and the fill valve will shut off automatically when the tank is full.

Flush the toilet several times and watch for leaks around the base, under the tank, and at the supply line connection. A small drip at the supply line connection usually means the nut needs another quarter turn with your wrench. If water pools under the base, the wax ring seal may not be complete—this is rare but means the toilet must be removed and reset with a new wax ring.

Once you confirm there are no leaks, explore a bead of caulk around the base of the toilet where it meets the floor. Use a caulk gun and silicone caulk rated for bathrooms. Smooth the caulk with a wet finger or caulk tool. Caulk prevents water from seeping under the toilet base and damaging the subfloor, though it also makes future removal slightly more difficult.

Common Mistakes to Avoid

The most frequent error is installing a toilet with the wrong rough-in distance. Measure twice before you buy. A toilet with a 10-inch rough-in will not fit in a 12-inch space, and forcing it will crack the base or leave gaps that allow water to escape.

Over-tightening the base bolts is the second most common mistake. The porcelain base is brittle and will crack if you use excessive force. Tighten until snug, then stop. The toilet will not move or rock when installed correctly.

Disturbing the wax ring after it is pressed onto the drain opening ruins the seal. Once it is in place, do not remove the toilet unless you are ready to replace the wax ring with a new one. If you accidentally lift the toilet, clean the opening and install a fresh wax ring before setting it down again.

Forgetting to turn off the water supply before disconnecting the line causes water to spray across your bathroom. Always shut off the valve first, even if you think the tank is empty.

When to Call a Plumber

If the drain opening is cracked, the floor is severely uneven, or the bolts are stripped and will not tighten, contact a plumber. These issues require repairs beyond a straightforward replacement. If water continues to leak from under the base after you have reset the toilet with a new wax ring, the drain flange (the fitting the wax ring seals to) may be damaged or misaligned—a plumber can assess this.

If your home has a septic system rather than a municipal sewer, confirm that your new toilet is septic-safe before installation. Some low-flow toilets are not compatible with septic systems. Your septic system documentation or a local plumber can advise you.

Frequently Asked Questions

How long does it take to install a replacement toilet?

Most people complete the job in two to three hours, including time to let caulk dry. If you encounter stuck bolts or need to make multiple trips for supplies, add another hour. The actual work—removing the old toilet and setting the new one—takes about 45 minutes once you have everything on hand.

Do I need a plumber's license to install a toilet myself?

No. Replacing a toilet with a new one in the same location does not require a permit or licensed plumber in most jurisdictions, as long as you do not modify the water supply line or drain. Check your local building code or contact your city's building department if you are unsure. Some areas do require a permit for any plumbing work.

What if the new toilet does not fit because the rough-in is wrong?

Return the toilet to the store if it is still in its original packaging and unopened. If you have already opened it, you may be able to exchange it for the correct size, though some retailers charge a restocking fee. Measure the rough-in distance carefully before buying to avoid this problem.

Can I reuse the old wax ring if I remove the toilet and put it back?

No. Wax rings are single-use. Once compressed and removed, they lose their seal and will not work again. Always use a new wax ring when reinstalling a toilet. They cost a few dollars and are essential to preventing leaks.

Why is water pooling under the toilet base?

The most likely cause is an incomplete wax ring seal. This happens when the toilet is not pressed down firmly enough or when the drain opening is uneven. Remove the toilet, clean the opening, install a new wax ring, and set the toilet down again, pressing down firmly at all four corners. If the problem persists, the drain flange may be damaged and require professional repair.