Sunday, November 6, 2011

How to Repair a Leaking Toilet Seal

This month we’re back in the bathroom with a leaky toilet. This time it’s an external leak (meaning that there's water on the bathroom floor) which, as we saw in the previous leak detection post, gives 2 basic possibilities:

1.       Leaks from the cistern – the toilet leaks and refills continuously causing an ever increasing amount of water on the bathroom floor.

2.       Leaks from the bowl or outlet – the toilet leaks during or after the flush leaving a small puddle on the floor. The quantity of water is limited since the cistern doesn’t refill.

The possible sources of these types of leak are:

1.       Leaks from the cistern

a.       Cracked or damaged cistern

b.      Leaky seal between the cistern and the pan

2.       Leaks from the bowl or outlet

a.       Cracked bowl

b.      Leaky toilet seal or flange

Cracked cisterns or toilet bowls can be repaired with an epoxy filler or repair-all type putty.

Damaged seals or flanges need to be replaced

Sometimes a good seal leaks because the cistern or bowl isn’t firmly fixed in place leak because of movement.  Check the bolts which hold the cistern to the bowl and the bowl to the floor are correctly tightened.  A toilet or cistern which rocks will often leak.

Visual inspection will show which of the causes mentioned above are to blame.

In this case we find drips coming from the toilet pan outlet seal. Closer inspection reveals that the rubber is perished and cracked. The solution is to replace the seal with a new one.

How to Replace a Leaky Toilet Seal

Toilet Repair Step 1

Fill a bucket, the sink and the kettle with water. We’re going to turn off the water at the main stopcock so we’ll need water to clean up, wash our hands (believe me you’re going to want to wash your hands several times during this process!) and of course make a cup of tea!

Toilet Repair Step 2

Turn off the water at the stopcock – there may be a small tap mounted on the wall at the inlet to the cistern, but in my experience these valves frequently leak. It’s always best to turn the water off at the stopcock.

Step 3

Flush the toilet to empty the cistern, undo the two plastic wing-nuts which connect it to the toilet bowl and lift the cistern clear (empty any residual water into the bath or the toilet and put the cistern carefully to one side)

Step 4

Remove the seal between the cistern and the toilet bowl. Depending on its condition you can either re-use it or replace it with a new one (Even thou the existing seal didn’t leak I decided that it would be a good idea to replace it with a new one when reassembling everything – preventive maintenance)

Step 5

Unbolt the pan from the floor. The are two bolts which fix the pan to the floor. We use a 10mm spanner to remove the cap-nuts. It’s possible that the nuts have corroded onto the bolts in which case the bolt will most likely release from the rawlplugs in the floor. If by a stroke of bad luck they don’t release easily from the rawlbolts in the floor then you may need to cut the nuts off using a dremel (or similar tool) and mini cut-off disk.

Step 6

The Toilet pan can now be lifted clear of the 2 fixing bolts and pulled away from the waste pipe.

Step 7

Tip the water from the toilet bowl into the bath.

Step 8

Remove the damaged toilet seal and (in order to ensure that the new seal seals) clean up both the outlet from the pan and the entrance to the waste pipe. Believe me, you will want to wash your hands after doing this!

Step 9

Remove the bolts from the floor; this is best done with mole grips. Take care not to damage the threads when doing this.

Step 10

Fit the new seal to the waste pipe and slide the toilet bowl into place, taking care to make sure the seal seats correctly against both the waste pipe and the exit from the toilet bowl.

Step 11

Replace the nuts and bolts which hold the toilet pan in place. Tighten down each side bit-by –bit to make sure that the toilet is correctly aligned and firmly seated.

Step 12

Empty the bucket of water into the toilet to perform a test flush and ensure that the new seal doesn’t leak. If it leaks, it will be necessary to disconnect the bowl again and re-seat the seal.

Step 13

If the toilet doesn’t leak then we proceed to re-connect the cistern and open the stopcock.

Step 14

Perform a test flush to make sure that everything works correctly and that there are no leaks.

Step 15

Clean up any mess and wash your hands!

Alternative Types of Toilet Seal

The rubber seal shown in the photos is very common. You may also encounter more elaborate seals or the old fashioned wax seal. In the case old the wax seal we simply cut the donut into two pieces, insert the two parts into the gap between the toilet and the waste pipe. We then use the heat from our hands to mold the wax into place until a hermetic seal is formed. The other plastic seal is simply inserted into the drain pipe and the toilet is slotted into place. Another possibility is that the toilet sits on-top of the waste pipe and there is a seal in a flange which is fitted into the floor below the toilet. These types of seal are similar to those which we have seen and the symptoms and replacement process are basically the same as described above.


  1. A leaky toilet is one of the most challenging repairs that any homeowner will face. It’s also quite expensive, and if you don’t have knowledge in repairing this, you’ll need an expert plumber to do it for you. Tip: When you’re repairing a leaky toilet seal, and you’re having a hard time putting the toilet back on the flange, you can attach plastic drinking straws to the bolts. Those can serve as your guides for the correct placement of the toilet.

    1. Hi Darcy,

      Thanks for your comment, I realy like your tip of using driking straws on the bolts to line the toilet up. I'll definately be using that trick in the future!

  2. A leak from the outlet or bowl is one of the common problems in the bathroom of many homeowners. This problem can cause structural damage to the floor and ceiling below. If water is leaking from the base after you flush the toilet, this could be because the wax seal is damaged. You must replace this wax seal immediately to keep the water after you flush from leaking.

    1. Hi Bibi,

      Thanks for your comment, I agree it's always best to fix leaks as soon as you notice them to prevent further damage!

  3. Are you a professional plumber or something? It seems like you really know how to fix a broken toilet seal following the proper procedure. But, you forgot to tell about the right wax ring to be used in a certain bathroom. For example, a wax ring with flange horn is best if your toilet flush sit is on the floor. On the other hand, a wax-free bowl gasket is best used in floors that are uneven.

    1. Hi Althea,

      Thanks for your comment. I apreciate you taking the time to share that additional information.

      I'm not a proffesional plumber - I'm a DIY enthusiast, although I used to work as a builder's laborer when I was a student and have fixed a few toilets over the years for family and friends!

  4. hello, i seem to have a problem with my toilet..i've used several sizes to fix it in the last months, but it still leaks..i checked the opening it is 5 1/2 " waste pipe and the rings only fit up to 4 1/2"..i think i have to get a pro to fix it, or do you know what i am doing wrong? the house was built in 1949..

    1. Hello,

      It is essential that you get the correct size of seal.

      I suggest that you take the original seal to your local hardware store so that they can match it. If they don't have one that is identical they should be able to order one for you or may be able to suggest a suitable replacement. If not try looking online.

      If you've already thrown the old seal away then you'll need to carefully measure the toilet outlet and the waste pipe, the make of the toilet and ask at the hardware store or plumbers supplies store, or check online.

      If it's the same type of toilet as shown in the photos above (where the outlet connects to the rear of the toilet rather than below) you could use one of the old style wax rings shown above instead but I recomend that you try and get the original seal. Alternatively modern EVA seals are so much easier to use and are available in a range of sizes and forms.

      If you really can't find a suitable replacement then I suggest you call a plumber. It's essential that you get the toilet to seal properly.

      I hope this helps

  5. It seems like you’re very handy with this kind of repair! I’ve looked into your previous posts about plumbing, and I’ve noticed that you handled several plumbing repairs previously. Well, experience is a great teacher, and the same goes with plumbing. Kudos to you, Richard!

    1. Hi Darryl,

      Thanks for your comment.

      I think that with a step-by-step approach and a bit of patience most people are capable of doing simple repairs like this round the home.

  6. Thanks for that - off to screwfix after work!

    1. Hi Karl,

      Thanks for your comment, it made me smile :-)

      Good luck!

  7. Having read all that on how to repair my toilet, I definitely need a plumber, so no trying to do it myself, but thanks for your useful tips. This is my first time on google,

  8. I hate the medieval idiots who designed these things. We can seal high pressure systems in cars and industry, but the gravity fed human waste reciprocal that NO-ONE wants to stuff around with leaks. Why can't they just use a flange and gasket.

  9. Thanks for your post. I suspect that the reason is manufacturing tolerances. In the case of cars and industry manufacturing tolerances are plus minus 0.1 mm whereas In the case of buildings the tolerance is plus minus and inch

  10. Thanks for your information. I'm a stay at home mum in Australia and I have just moved into a new ' old ' house. I have already fixed the leaky seal between the cistern and the bowl. I'm struggling with the next leak between the bowl and the back outlet pipe. However your process is very helpful so I'm going to give it a go. Cheers mate☺

    1. Thanks for your comment, I'm glad you found the post useful.

      Good luck and don't forget to let us know how you get on.