If you haven’t read the first four parts of this series, take a moment and do so, as they address some of the most common problems. Here are the links:

• How To Fix A Running Toilet, Part 1
• How To Fix A Running Toilet, Part 2
• How To Fix A Running Toilet, Part 3
• How To Fix A Running Toilet, Part 4

But if you still can’t figure out why your toilet is running, check out this simple diagnostic test. It’s an almost fail-proof way to test a toilet flapper, but only when you’ve ruled out the possibilities discussed in earlier sections.

Step Nine: Put Food Coloring Into The Toilet Tank.

Use enough to change the water’s color, but don’t use so much that it stains anything. Once you’ve done that, let your toilet sit for an hour or so (and don’t use it!), then examine the toilet bowl. If you notice a hint of color, there’s a good chance your flapper is leaking.

(Note: Plumbing stores often carry a special dye for this purpose, and it is priced relatively cheap, but food coloring usually works just as well and costs much less.)

You’re probably asking, “If the flapper is leaking, why didn’t I notice it earlier?” Sometimes the leak is so subtle that you won’t feel it at all with your hand. But the fact that the water from the tank ended up in the bowl (after you’ve ruled out other possibilities) is almost a tell-tale sign that the flapper is leaky.

If you’ve got a leaking toilet flapper, replace it! It’s an extremely easy fix and the shouldn’t cost a do-it-yourself plumber more than a couple of dollar in parts. And since flappers are almost always the culprit of running toilets, it might be worth your time to change it out even if you DON’T think it’s the problem.

Still can’t put an end to your running toilet blues? Read Part 6.

If you haven’t read How To Fix A Running Toilet, Part 1 yet, it’s worth a look. It explains just how costly an unfixed running toilet can be. Read Part 1 here.

Step One: Jiggle the handle.

This might seem basic, but don’t underestimate how many times this solves the problem. Granted this is usually just a quick fix and merely a case of fixing the symptom rather than the problem, there are cases when a toilet will randomly run even if every part is in perfect working order.

If this solves the problem, congrats! But keep a mental note of the toilet’s performance. Even though perfectly fine toilets will randomly run here and there, frequent running is likely a sign of a further problem.

Step Two: Check the tank.

Take the lid off the toilet tank and take a look inside. Sometimes debris of some sort is preventing the flapper from completely closing. This is a common problem for those who use in-tank toilet cleaning products that gradually disintegrate over time. These have a tendency to move around, and sometimes end up causing problems with the flapper.

Sometimes excess slack in the chain can interfere with the flapper valve, too.

Even if the flapper appears to be properly seated, give it a quick ‘feel test.’ With the valve down, run your finger along the flapper seal (in a circular motion). While doing this, pay attention to any areas that seem to be leaking. You should feel a small vacuum effect as your finger covers up a leaky spot.

Step Three: Flush the toilet.

Give the toilet a quick flush. Watch the flapper – does it open completely? If not, its hinge might have worn out. Check the opening, is any debris present? If so, remove it. Even if there isn’t enough water in the tank for a complete flush, opening the flapper often reveals many easy fixes.

No dice? Continue on to Part 3.