How to Fix a Running Toilet in Your NYC Apartment

Before You Start

A running toilet wastes 200+ gallons of water per day. In NYC, where water is metered for most buildings, that's real money going down the drain. The good news: 80% of running toilets are fixed by replacing a $5 flapper. You don't need a plumber for this.

Step 1: Diagnose the Problem

Take the lid off the tank and look inside. You'll see two main components: the fill valve (tall piece on the left, connected to the water supply) and the flush valve (center, with a rubber flapper at the bottom).

The food coloring test: Drop 5-6 drops of food coloring into the tank water. Don't flush. Wait 15 minutes. If colored water appears in the bowl, your flapper is leaking. This is the most common cause.

If water is running over the top of the overflow tube (the tall tube in the center), your fill valve is set too high or is malfunctioning.

Step 2: Replace the Flapper (Most Common Fix)

The flapper is the rubber seal at the bottom of the tank that lifts when you flush and seals when it closes. Over time, the rubber warps, hardens, or gets mineral deposits, and it stops sealing properly.

Shut off the water supply valve behind the toilet (turn clockwise)

Flush the toilet to empty the tank

Unhook the old flapper from the ears on the flush valve and disconnect the chain from the flush handle

Take the old flapper to the hardware store and match it - NYC hardware stores carry universal flappers, but matching the exact size ensures a good seal

Hook the new flapper onto the flush valve ears, connect the chain to the handle lever with about 1/2 inch of slack

Turn the water back on and let the tank fill

Flush and watch - the flapper should seal completely with no water trickling into the bowl

NYC apartment tip: If your shut-off valve behind the toilet is a gate valve and it's old, it might not fully close. If water still trickles with the valve "closed," don't force it. Work quickly with the supply on and keep towels handy. Or call your super about replacing that valve.

Step 3: Adjust or Replace the Fill Valve

If the food coloring test was negative but water is running over the overflow tube:

Look at where the water level sits in the tank. It should be about 1 inch below the top of the overflow tube

Most fill valves have an adjustment screw or clip on the shaft. Turn the screw counterclockwise or slide the clip down to lower the water level

Flush and check that the water stops at the right level

If adjusting doesn't work, the fill valve needs replacement. This is a $10-15 part and a 30-minute job:

Shut off the supply valve and flush to empty the tank

Disconnect the supply hose from the bottom of the fill valve (have a bucket underneath)

Unscrew the locking nut on the bottom of the tank

Remove the old fill valve, drop in the new one, tighten the nut

Reconnect the supply hose with plumber's tape on the threads

Turn water on and adjust the water level

Step 4: Check the Handle and Chain

Sometimes the fix is even simpler. If the chain connecting the handle to the flapper is too short, the flapper can't fully close. If it's too long, it can get caught under the flapper.

Adjust the chain so there's about 1/2 inch of slack when the flapper is seated. Cut any excess chain to prevent tangles.

When to Call a Plumber

The toilet rocks when you sit on it (the wax ring seal may be broken, which requires pulling the toilet)

Water is leaking from the base of the toilet onto the floor

The shut-off valve doesn't work and you can't stop the water

You're in a co-op or condo and your building requires licensed plumber work for any modifications

NYC-specific: If your building has no individual toilet shut-off valve and you need to stop water flow, you'll need the super to close the riser valve. This shuts off water to multiple apartments. Another reason to make sure your shut-off valve actually works before you need it.