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A weak flush is one of those problems people live with for years. The bowl swirls lazily, paper comes back up, and everyone in the house learns to hold the handle down. It is almost always one of a handful of causes, and none of them needs a new toilet.
First, is it the drain?
Pour a full bucket of water into the bowl quickly. If it goes down with a strong flush, the drain is fine and the problem is in the tank. If it drains slowly or backs up, the problem is a partial blockage in the toilet or beyond it, and a toilet auger is the tool, not the tank.
Cause 1: not enough water in the tank
Take the lid off. The water level should sit about an inch below the top of the overflow tube, and many tanks have a line marked inside. A tank that fills too low delivers a weak flush every time.
Raise the float. On a modern fill valve, there is a screw or a clip on the side; on an older ball float, turn the screw on top of the valve or gently bend the arm up. Flush and check the level again.
Cause 2: the flapper closes too early
Watch the flapper during a flush. It should stay up until most of the tank has emptied. If it drops back after a second, the flush is cut short.
- The chain has too much slack. Shorten it so that there is about half an inch of slack when the flapper is closed.
- The flapper is the wrong type. Some flappers are adjustable, with a dial or a float on the chain that sets how long they stay open. Set it for a longer flush.
- The flapper is worn. After a few years the rubber stiffens and no longer rises cleanly. A new flapper costs a few dollars.
Cause 3: blocked rim holes
Water enters the bowl through a ring of small holes under the rim, and often a larger jet at the bottom. In Rockland's fairly hard water, mineral scale gradually closes them, and the flush loses its swirl.
- Hold a small mirror under the rim to see the holes.
- Clear each one with a piece of stiff wire or a straightened coat hanger, and the bottom jet with the same.
- For heavy scale, close the toilet's shut-off valve, flush to empty the tank, then pour a bottle of white vinegar down the overflow tube and leave it overnight. The vinegar sits in the rim channel and dissolves the scale. Flush in the morning.
Cause 4: a partially blocked trap
Something that should never have been flushed, such as a toothbrush, a toy or a wipe, can lodge in the toilet's internal trap and let water past, but slowly. A toilet auger reaches it. If the auger meets nothing and the flush is still weak, the object may be beyond the toilet, and a plumber's camera will find it.
Cause 5: the vent
Every drain needs air behind it to flow. If the vent pipe on the roof is blocked, by leaves, a bird's nest or snow, toilets flush weakly and drains gurgle throughout the house. Look at the vent from the ground. Clearing it means going onto the roof, which is a job for someone comfortable doing that, or a plumber.
About older low-flow toilets
Toilets made in the first years after the 1.6-gallon rule came in, roughly the mid 1990s, were often poor. If yours is from that era and none of the above helps, a modern toilet will flush far better on the same water. Replacing a toilet is within reach of a capable homeowner, and a plumber can do it in an hour or two.
When to call a plumber
- Several fixtures are slow at once
- The toilet leaks at the base, or rocks
- A blockage beyond the toilet that the auger cannot reach
- A blocked roof vent you cannot safely get to
Find a licensed plumber near you.