Short definition
A toilet (water closet, WC) is the gravity-flush sanitary fixture that drains into the building’s DWV system through a closet flange and wax ring. The tank holds the next flush; the bowl holds the trap. Pull the handle, the flapper opens, water drops into the bowl, the siphon empties the trap, and the fill valve refills both. The two things that break are the flapper (won’t stop running) and the wax ring (leak at the base).
What it is
A residential toilet is a tank-type, gravity-flush fixture with three subsystems.
Supply side. Cold water enters through an angle stop (shutoff valve) on the wall, then a flexible supply line, then the fill valve in the tank. The fill valve is the part that hisses after a flush; older homes have a brass ballcock, modern tanks use a diaphragm or float-cup design. A small refill tube runs from the fill valve into the overflow tube to top off the bowl after each flush.
Flush mechanism. Pulling the trip lever lifts the flapper (or canister) off the flush valve seat. The tank empties into the bowl through the bowl rim and a jet at the base of the bowl; the rush of water primes the trap and siphons the contents into the drain. When the tank empties, the flapper drops back onto its seat and the fill valve refills the tank.
Drain side. The bowl bolts to the floor over the closet flange — a fitting that anchors the toilet to the building drain. A wax ring (or wax-free seal) compresses between the toilet horn and the flange to make the joint gas- and water-tight. Two closet bolts hold the bowl down.
The integral siphon-jet trap inside the bowl is what gives a toilet its standing water. That trap seals out sewer gas the same way a P-trap seals a sink.
Why it matters to a homeowner
Toilets get used more than any other fixture in the house, and almost every part of one is replaceable in twenty minutes with a wrench. The two failures you’ll see most:
- Toilet won’t stop running. The flapper is leaking — a $5 part. If a new flapper doesn’t fix it, the fill valve is the next suspect. See toilet running.
- Water on the floor at the base. Wax ring failure, loose closet bolts, or a cracked/rotted closet flange. Pull the toilet, replace the wax ring, reset. See water on floor around toilet.
When you replace a whole toilet, two dimensions decide which models fit:
- Rough-in — distance from the finished wall to the centerline of the closet flange. Standard is 12 inches; older homes (and some bathrooms with framing constraints) have 10 or 14 inches. See toilet rough-in.
- Bowl shape — round-front (shorter) or elongated (about 2 inches longer, more comfortable). Measure the floor space first.
Common variants and not the same as
- One-piece vs. two-piece. One-piece toilets are a single ceramic casting — easier to clean, more expensive, heavier. Two-piece bolt a separate tank to the bowl with a tank-to-bowl gasket; cheaper and easier to fit through doorways.
- Standard height (about 15″) vs. comfort height (17–19″, ADA). Comfort height is the default for aging-in-place remodels. See comfort-height toilet.
- Round-front vs. elongated bowl. Elongated is more comfortable; round-front saves about 2 inches of floor space.
- Single-flush vs. dual-flush. Dual-flush toilets give you two button options (typically 1.6 / 1.0 GPF). See dual-flush toilet.
- Toilet vs. bidet vs. bidet-toilet. A bidet is a separate fixture or seat for water cleansing. See bidet and bidet-toilet.
Common failure modes
- Running toilet — flapper isn’t seating, fill valve isn’t shutting off, or chain is too short.
- Phantom flush — slow tank-to-bowl leak (often a worn flapper); confirmed with a toilet dye test.
- Weak flush — clogged rim jets, low water level, partial flapper close, or a clogged trap.
- Leak at the base — failed wax ring, loose closet bolts, broken flange.
- Tank-to-bowl leak — failed tank-to-bowl gasket / spud washer.
- Rocking on the floor — uneven floor; needs toilet shims under the base, not extra caulk.
- Tank sweating — cold supply against warm humid bathroom air; an anti-sweat tempering kit or a tank insulation jacket fixes it.
Flush rate (1.28 GPF, 1.6 GPF, or higher)
Federal law caps new toilets at 1.6 gallons per flush since 1994. WaterSense-labeled models flush at 1.28 GPF or less. Pre-1994 toilets often flush at 3.5 GPF or higher — a single-fixture replacement saves roughly 13,000 gallons per year for a family of four. In Washington, new-construction permits require WaterSense-compliant fixtures under the state energy code; remodels that go through permit follow the same rule. See toilet flow rate 1.6 / 1.28.
FAQ
How long should a toilet last?
The porcelain itself lasts decades — often longer than the house’s other plumbing. The internals (flapper, fill valve, supply line) wear out on a 5–10 year cycle. The wax ring lasts as long as the toilet stays put; it fails the moment the toilet rocks. Most full-toilet replacements are driven by remodel choices (comfort height, low-flow, style), not because the bowl wore out.
Can I install a toilet myself?
Yes. A toilet swap is a standard DIY project: shut off the angle stop, drain the tank, disconnect the supply, unbolt the toilet, scrape the old wax, set a new wax ring, drop the new toilet onto the closet bolts, level and shim, tighten gradually in a cross pattern, reconnect the supply, and turn it back on. Two-piece toilets are easier than one-piece because of weight. WA does not require a permit for a like-for-like residential toilet replacement.
What does GPF mean?
Gallons per flush. The legal maximum for a new toilet sold in the US is 1.6 GPF; WaterSense-labeled toilets are 1.28 GPF; some “high-efficiency” models flush at 1.0 GPF. Older toilets (pre-1994) flush at 3.5–7 GPF. The lower numbers save water but are more sensitive to drain-line slope and clogged rim jets — hence the focus on bowl design (siphon-jet, pressure-assist, dual-flush) in the EPA-compliant generation.
Is a wobble dangerous?
Yes — a rocking toilet flexes the wax ring and eventually breaks the seal at the flange. The fix is shims under the bowl, then re-bedding the wax ring if the seal already broke. Don’t caulk over the rocking; that just hides a slow leak that rots the subfloor.