Toilet Will Not Flush or Drains Slowly

It separates a drain problem from a tank problem in one minute.

Pour a bucket of water into the bowl quickly, from about waist height. If it clears briskly, the drain is open and the fault is upstream in the tank or the rim jets. If the water rises and drains slowly or not at all, the problem is the trap or the drain line, and no tank adjustment will fix it. Do not pour if the bowl is already near the rim.

A flush needs its full volume to start a siphon.

Lift the lid and compare the resting water level with the line moulded into the tank or marked on the overflow tube. A level set too low delivers a partial flush every time, and it is one of the most common causes of a chronically weak toilet. Adjust the float to the manufacturer mark rather than to a guess.

A flapper that closes early cuts the flush short.

With the lid off, flush and watch. The flapper should stay open long enough for the tank to empty, then seat cleanly. One that drops early releases only part of the tank; one that never seats leaks continuously, which is a separate and expensive problem covered in the running toilet guide.

Mineral deposits close the holes that aim the water.

Water enters the bowl through small jets under the rim and, on most designs, a larger siphon jet at the bottom. In hard-water areas these narrow with scale, so the same volume arrives too slowly to start a proper siphon. Inspect them with a mirror and a light; a flush that trickles down one side of the bowl is the classic sign.

A single slow fixture and a whole slow house mean different things.

If only the toilet is slow, the obstruction is likely in its trap or the branch. If sinks, tub, and toilet are all slow, or drains gurgle when another fixture runs, the main line or the vent is involved and that belongs with a plumber. Avoid repeated chemical drain products, which can damage fixtures and make later mechanical clearing hazardous for whoever does it.