How to replace the diaphragm in a toilet cistern siphon

Often, the problem with a toilet not flushing properly lies in the cistern.

The siphon, indicated in Figure 1, is normally at fault.

Figure 1:  Siphon inside a toilet cicstern

It contains a washer, known as a diaphragm, which disintegrates with age and use.

To replace it, follow these instructions carefully.

First, switch off the cold water supply.

Lift off the lid of the cistern.

If possible flush the existing water away.   (If you cannot flush, then you will need a sponge to completely empty the cistern.)

Then disconnect the water feed pipe, using a spanner - as in Figure 2.

Figure 2, disconnecting the water feed pipe from a toilet cistern, using a wrench.

Next, remove the two locking nuts connecting the cistern to the toilet bowl.   (Figure 3)

Figure 3 - butterfly locking nut that attached the toilet cistern to the toilet bowl

Remove the two screws holding the cistern to the wall:

Figure 4:  removing a screw holding the cistern to the wall

The cistern will now lift clear of the toilet bowl.

Then remove the washer and locking nut from under the cistern.

Figure 5:  Washer underneath cistern
Figure 6:  Locking nut

Next, remove screw holding the flush handle to the siphon.

Figure 7:  screw holding flush handle to the siphon.

This may be rusted, and need some help from a pair of pliers:

Figure 8 - using pliers to loosen a rusted screw from a toilet cistern

Slide the flush-lever (the black one shown in figure 8) from the handle, and remove the siphon:

Figure 9:  the siphon, removed.

Inspect the diaphragm for damage.   In Figure 10 the diaphragm is the blue plastic floppy washer, and in this case, the damage can clearly be seen.

Figure 10:  damaged diaphragm - these disintegrate over time

In some cases, it may be necessary to replace the entire siphon, but in this case we will replace only the torn diaphragm, which can be purchased separately.

Remove the coupling pin from the top of the plunger, as indicated in figure 11.

Figure 11:  the coupling pin

Depress the plunger and remove the housing:

Figure 12:   push down on the plunger
Figure 13 - removing the diaphragm  housing

Be careful not to lose the spring:

Figure 14 - removing the spring.

Next remove the washer holding the diaphragm, using a flat screwdriver to prise it off:

Figure 15 - prising the washer which is
holding the diaphragm in place
Figure 16;  the loosened washer

Lift off the diaphragm

Figure 17:  lifting off the diapgragn.

The damage here can clearly be seen:

Figure 18 damaged toilet syphon diaphragm

Replace the diaphragm.

Figure 19:  this replacement diaphragm is made of clear plastic

Put back the locking washer.

Add the spring.

Replace the diaphragm in the siphon housing, and replace the coupling.

Insert the siphon into the cistern, and replace the locking nut.

Replace the cistern onto the toilet bowl, ensuring you have the sponge washer in place.

Figure 20;  sponge washer under the toilet cistern.

Replace the two screws holding the cistern to the wall.

Also replace the two butterfly locking nuts which fasten the cistern to the bowl.

Replace the coupling pin between the siphon and the flush-handle - ensuring that the flush-handle is at the original angle - as seen in Figure 21.

Figure 21:  coupling pin between the siphon and the flush handle.

When reconnecting the water supply, it is recommended to wrap plumbers' tape around the threads of the pipe:

Figure 22:  wrapping the threads with plumbers tape

Figure 23 - the wrapped pipe threads

Reconnect the water supply to the cistern

Figure 24:  reconnecting the water feed pipe.

Turn on the water, and check for leaks:   be prepared to turn off the water again if necessary, and tighten any connections.

Now flush the cistern, to test that it's working correctly.

Job done. Well done.


  1. Clear, simple instructions with good photos. Thank you very much!

  2. If you are ultra-cheap or in a hurry - you can cut out a replacement diaphragm using an old plastic milk container

  3. simple and clear instructions thank you so much

  4. Thanks for the clear guidelines. However, my siphon, and probably all modern siphons, has a plastic pin located at the top of the siphon which allows you to dismantle the siphon, in order to replace damage parts. Consequently, you do not need to disconnect the cistern tank, saving much time and effort. The siphon used in the illustration is a sealed unit, so before you go through the rigmarole of dismantling the cistern tank check first the top part of the siphon to see whether you can dismantle it from the tank.

  5. These guidelines are clear and consise. The siphon in the illustrations appears to be a complete sealed unit. I have what appears to be a more modern type, which means that instead of having to dismantle the cistern tank, you can instead simply dismantle the siphon from inside the tank. Near the top part of the siphon (the side of the siphon which leads down into the pan) there is a plastic pin which you can take out allowing you to take out the part of the siphon containing the diaphragm. Once the diaphragm had been replaced you can simply put it back in place and put the plastic pin through. So before you take off the cistern tank first check the siphon to see whether you can dismantle it from within the tank.

  6. Here is a picture of the dismantled siphon and I'm pointing to the plastic pin you pull out to dismantle it.

  7. Good blog, but it would be much easier too use a 1/2" to 15mm flexi tap connector to connect to the ball valve.

  8. Great guide and photos. MJ Ireland

  9. Done and dusted in under an hour....not bad for a girl. Thanks SO much for your crystal clear instructions and spot on photos.

  10. Generally as I would do the job but I would not waste my time putting ptfe tape around the threads of the connecting joint. this has no bearing on making the joint watertight.. Wrapping tape around the face of the olive (contact side as you insert into valve base) will give a better result. Usually a cut up milk carton is too rigid to work well, I find that a heavy duty plastic sack (merchant's sand or gravel bag is more suitable if nothing else to hand.

    1. I used a piece of pond liner to make one using the old broken one as a template - this material won't split or buckle and is very strong but pliable, so is ideal for this purpose.

    2. I made a replacement diaphram for a ceramic Armitage cistern from an old car inner tube and the backing disc (which was ceramic and broken) from a piece of 6mm ABS plastic

  11. Fixed a troublesome toilet myself and i hate plumbing thanks !!!

  12. Thank you for such clear instructions and photos. Have fixed my toilet for £1 instead of having to pay for a plumber !!!

  13. Great instructions for doing a job yourself and saving many pounds by not using a plumber. Many thanks and keep up the good work!

  14. Thank you. It worked perfectly. My local store did not have the correct sized diaphragm, so I made my own using a plastic milk bottle and the damaged diaphragm as a template.

  15. Thank you so much for this. Luckily my siphon was the open kind. Managed to do it all first using a milk bottle to create the diaphragm then was completely disheartened when it didn't work! Tried again using a more flexible plastic (a staples heavy duty document wallet) and it worked! If a complete DIY idiot like me can do it anyone can. Excellent instructions thanks again

  16. Followed your guide and fixed my toilet. Feeling very pleased with myself now!! Many thanks for these wonderful instructions, allison

  17. I could not find ANYTHING on the web regarding splitting a 3 part syphon, which means you dont have to mess about turning the water off etc, the 2 parts of it come apart from one another, with either a clip or nut, undo the handle connector from it, remove, and replace diaphram or washer/spring as required. Spring was snapped on the one I looked at, stretched spring out as a temp fix, job is a good un! Thanks for the advice anyways! But simpler and easier than stripping everything...

  18. Thanks for these brilliant instructions. We had the added complication of a rusted on wing nut on one of the bolts holding the cistern to the bowl which meant the plumber I called wanted to disconnect the whole toilet bowl. I read your great instructions and in addition to a new diaphragm we bought a replacement kit with bolts, wing nuts and sponge washer and having looked at your instructions I was confident to saw through the connecting bolt, which took a while, but now all is good as new. I would have replaced the siphon with a multi-part one for ease of future maintenance but the shop we went to only had sealed units. Thanks again for the instruction s and making this a doable job for me.

  19. Brilliant! Had no idea about toilets before but your guide allowed me to fix ours in half an hour (including the drive to the plumbing supply place).

    Now to open a beer and wait for the wife to get home and lavish me with praise.

  20. Victoria- Powys, Wales.November 27, 2015 at 4:50 PM

    Thanks for the clear instructions. I had a bit of trouble undoing the locking nut as it was all a bit rusty down there . I had to buy a couple of wrenches, the diaphragm ,a new ( non-rusty) coupling kit and some washers, so it cost me £25, but I'm still very pleased I did it .

  21. Thank-you for your excellent instructions. I have replaced my damaged diaphragm with one made from a milk carton and it works perfectly.

  22. Brilliant Thanks for your time

  23. Great instructions! I just took out the syphon and the diaphragm looks good so now I'm wondering when I still have a weak flush? Should I replace the whole syphon? Thanks!

  24. Hi there, toilet repaired for 60p!! thanks to this site and to the persons comments about taking the syphon out without dismantling the toilet. Thank you Thank you

  25. Discovered fault to be failed diaphragm the syphon unit was a twopart unit that could be removed for maintenance Went to local wicks but no suitable spare bits so lashed out on new unit @ £5.00 which was a pain cause It required me to remove the cistern all fixings replaced no leaks.I have then read this DIY how to help page.I have refurbished the old unit using a stout plastic sack that my bird seed came in tested in the bath

  26. Fabulous instructions, thank you. I managed to follow them exactly and changed the diaphragm. The only extra bit I would have liked was how to fix a leak even after tightening the coupling washer. I had to call a friend's husband who came with some kind of waterproof putty which he applied around the screw of the siphon so that the coupling nut then sealed.
    I had no idea such a thing existed. Having said that, the toilet in question is more than 15 years old, so some wear and tear is to be expected.

  27. Absolutely brilliant. Each step covered. Very clear.
    Had to buy pack of 5 diaphragms.
    Thank you

  28. Many thanks for taking the time to create these tips, very much appreciated.

  29. Great instructions. Plumber quote £75 as a Saturday. Actual cost 79p plus half an hour of my time. Bargain! Thank you.

  30. the spring has snapped on mine does anyone know where i can get one thanks

  31. Thank you so much for these brilliantly clear instructions. I found that I had the multi part siphon and - like a previous poster - could find no help on the web for one of these so I'll describe what I did in case it helps someone else. I used your instructions and my noggin and disconnected the wire pull lever (had to unscrew the handle to swing it out of the way) then pulled out the yellow plastic split pin to loosen the business part of the siphon. When I first saw the diaphragm, I thought that it looked okay but once pulled apart, the huge split was obvious. I cut a large rectangle from a plastic envelope folder that is usually used for documents and that seemed to be about the equivalent thickness of plastic. (Thanks to whoever suggested that.) Next, I cut a hole in the centre and slipped it over the post that holds the spring then cut round it to match the plastic shape. I recalled seeing a chap draw round a damaged diaphragm on another website and remembered him saying to leave about 1/8th inch all round so I did. Once put back together, it all worked beautifully so thanks a million for all your good advice and clear illos. They were very much appreciated by this little old lady pensioner - especially as it cost nothing.

  32. Thanks so much, easy to follow instructions. Nice one! My loo flushes again, yay!

  33. followed instructions thank you very much but toilet is leaking should I use some kind of sealant. many thanks for any answers

  34. Have done it before - got so far, couldn't remember how to get the unit out of the siphon (was over 5 years ago and if you don't do it regularly......!) resorted to googling and your site came up. Memory jogged and completed job ok. Thanks for posting it. regards Gillian

  35. How do you get around a toilet that has female thread in it, so syphon screws directly into it? Bought a syphon that comes apart but to wide to fit in tank, bought another then couldnt turn syphon body to screw into toilet?

  36. Excellent. Saved me the cost of a plumber, did the job myself for £4.99.

  37. Took a bit longer than 30 minutes due to rusted on everything but this article gave me the confidence to keep at it. Piece of gash plastic for a diaphragm and all done. Cost - nothing but a couple of hours of my time. Thanks Jock, one of the best explained posts I’ve seen.

  38. Thank you for this great advice.....was quoted £162.78 for fixing my cistern, and the plumber refused to do it on first visit because he claimed that the wing bolt had to be cut off (it didn't actually) I found your page, did it myself using a piece of plastic from a dog food bag as a replacement diaphragm, and a replacement close coupling kit....all for £6.90!!!

  39. Really clear instructions thanks, although i didnt see the need im my case to remove cistern from wall. I can't understand why the diaphram is made of such flimsy plastic though? I bought a flimsy clear plastic replacement part but still ended up following the advice left in a comment on here and used a plastic milk carton, the flush is much better.

  40. These instructions are brilliant - clear, easily understood and the photos make it very easy to follow and understand.

    I would add one step which I have learned through a problem happening to me: when replacing the siphon in the cistern, it is really important to clean around the whole where the siphon goes through the bottom of the cistern. I replaced the washer and the siphon, put everything back together and had a slow leak coming from that hole. When I dismantled everything again, I found old mastic and grime around the hole on the inside of the cistern. I cleaned that off and then put some fresh mastic around the hole, pressed the washer into it, allowed it to go off for a couple of hours and then put everything back together.
    Hope this helps someone else!


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