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I have a toilet that about half of the time doesn't flush fully, but will always flush fine on the second attempt. It does this regardless of the "contents" in the bowl.

I first took a plunger to it, but it didn't help at all. I then came here and read How can I fix a toilet that flushes incompletely? and looked inside the tank while flushing and the flapper seems to be functioning normally. I then read Why do my toilets flush slowly and often incompletely? and cleaned up everything like Inkspeak mentioned in his answer, but still hit or miss. I am starting to wonder if my toilet is as bad as Inkspeak says one of his three toilets were.

I bought this house just a few months ago and it has been happening the whole time. The house was built in 2007 and this is the only toilet that is having the issue. Is there anything else that I could try before I just replace the whole toilet? It seems like the toilet is young enough that it shouldn't have too much build up in it, but I also know that we have rather hard water based off of how fast we see mineral build up in our shower that we didn't see in our previous house.

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    If your house is that new, then it almost certainly has water-saving toilets installed, and the cheaper water-saving toilets simply don't work too well. We had one that you had to flush three times to have any result, which of course thoroughly negated the low gallons-per-flush. Replaced it with a higher-end toilet (researched and found one that was rated excellent on flushing performance) and have had no further problems.
    – Martha
    Jan 5, 2012 at 15:55
  • A possible mitigation until a solution is found is to keep a spray bottle of diluted dish detergent on the back of the toilet and sprits 3-4 times before flushing. This breaks the surface tension of the water making it much easier to drain out. Been doing this for about a year on an old toilet that I'll replace when I can.
    – DocSalvager
    Feb 14, 2018 at 12:07

4 Answers 4

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If the problem is mineral clogging of the under-rim channels on the toilet, and this does produce the symptoms you describe, then neither CLR no vinegar may be enough to clear up the blockage. The traditional treatment is a cup or two of muriatic acid (HCl 36%, from the hardware store) down the overflow hole in the tank. That goes directly to the rim vents. Pour the stuff in, wait an hour, and flush. Gloves and eye protection are recommmended, and a funnel so as to avoid spillage and corroding the metal parts in your tank. This looks like decent writeup of the method: How to Fix a Slow Toilet

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  • Gloves and eye protection are definitely recommended. Muriatic acid is just another name for hydrochloric acid, which is one of the strongest acids there is (depending of course on the concentration of the solution). Read all the instructions, etc.
    – Craig Tullis
    Jan 6, 2016 at 6:08
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I will describe the test you need to do to check the toilet.

  1. Remove the tank cover, be sure the tank is full of water to the full mark.
  2. Push the flush handle.
  3. When the rubber flapper flips up, reach down and hold it in the up position until all the water has drained from the tank.

If the toilet flushes completely under this test, but not on it's own, then your flapper is closing too soon, or the tank is not filling as much as it needs to do. The flapper is a real easy replacement, if the tank is not filling, then the fill valve needs to be replaced.

If it did not flush completely, time to spring and spend 200 bucks for a new Class 5 toilet. Which toilet to buy is a whole new topic.

Good luck.

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  • Why would you need to hold the flapper open? Shouldn't depressing the flush lever and holding it accomplish the same thing?
    – Captain Prinny
    Feb 15, 2022 at 13:24
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I had exactly the same problem and was able to figure out why it was working on the second time and thus fixed the issue. In order for the toilet to flush there has to be a sufficient amount of water in the bowl before flushing. In my case, when I was flushing the first time, water would stay in the bowl and therefore, when the second flush came in, it would all go down properly. But at that point while the tank filled up, no water would go into the bowl and the level of water in it, needed for the next flash, would be too low. When I looked inside the tank, I noticed that the incoming water was sipping through the intake valve and did not create enough pressure in the overflow valve to spill back into the bowl. It turned out the gasket in the intake valve was too old and fell apart. Replacing gasket would solve the problem, but I had to replace the intake valve as my hardware store didn't have the gasket I needed.

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It could be something to do with your OFV. The water is not filling up right to the touch point of it. This is why your water is not filling up the cistern and not got enough to flush your toilet

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