How to Change a Toilet Flush or Syphon Unit – Plumbing Tips

Posted by in Plumber Talk, on September 8, 2017


This video shows you how to change a toilet flush or syphon unit. Including the toilet seal or donut and the clamp that holds it all together. For more information visit our website at

HOLLA! Welcome to this video. Today I’m going to show you how to change a flush unit or syphon unit on your toilet. BIG and LARGE!! This toilet’s having a dire time flushing so we need to change the syphon unit ASAP. First thing we do is turn the water softener right off. Lift up the top of our beast, check that we’ve got no water coming through by dipping the ball valve. Then we try and get the toilet to flush. Get rid of that water in the chamber. Now we’ve still got quite a bit left in there so now we need to use a towel. Dip it in the chamber to try and get all that water out. Or you can effectively cheat and instead of trying to towel all that out you undo the 2 screws on the bottom that hold the doughnut and clamp together and lift up the whole cistern off and try and pour all the water away into a bath. Undo these screws here that can be really tight. unfortunately these particular screws have been on there for such a long time that I’m going to have to hacksaw them off. Once you’ve got those 2 screws taken off remove the cold feed and the overflow pipe.
So here’s our cold feed get yourself a set of adjustables round there.
Unscrew. Go round to this side Look in the top you’ve got your overflow bit there. That comes out down here, should just unscrew by and Unscrew that Now what we need to do is remove these screws here and get these one’s out. These are what hold the cistern to the wall. In this case because it’s quite an old building we’ve got some batoning here to hold the cistern in place Right, so now the toilet’s effectively, well the cistern is effectively removed from the toilet, we’ve disconnected our waste, I mean our overflow, we’ve disconnected our flow and we’ve taken the 2 screws off at the bottom that hold the doughnut and clamp together and we’ve taken the 2 screws off at the back that hold the cistern to the wall. Now we should be able to just pop this up and it should just lift off. Makes a lovely noise! There we go. Now it’s full of water so I’m just going to take it over the the bath and tip it all out. Get a towel put it over your toilet here and put this here for operation. Right, this is the bottom end of the toilet. This is the doughnut. Take this off. Generally when you’re changing a flush or syphon unit change this doughnut. And this is the clamp where your screws slot into here and they compress the doughnut onto the toilet into the cistern creating a watertight seal. Get ourselves a set of grips and pop them on here and then just loosen this nut off and take this right off. As you can see you’ve got a lot of scale on there which can get on the thread and make it a bit difficult. This one’s coming off alright. Pop this off. Now that means the syphon unit in there is now loose. If you have a look in there we have the flush handle that pulls the syphon unit flush up. So now we take this bit out here and remove the whole flush unit like so and remove it off the hook off the flush clip. The exciting bit. A new flush unit and a new doughnut and clip. Take this moment to quickly see how a syphon unit works. It sits in your toilet like this. Water fills up to about here and goes past this flap, rubber flap, in here. When you pull this up and your flush the toilet all this water is pushed up down there and that downward pushing suction there creates a syphon which, in turn, sucks it up to the point where air gets in here and breaks the syphon and that’s how they work. Let’s see how you put one back in. Firstly you get your washer and pop that over the end Make sure that the inside of the toilet cistern is smooth and there’s no limescale under there otherwise you won’t get a watertight seal.
Right, so we hook the new syphon unit on to this clip here pop it through the hole and you can see then from looking through here that’s what happens. Now we’ve got the new syphon unit in place. This is the doughnut clamp. Pop that on there like that. Right, now we get the new nut and pop that on here and that clamps the 2 together. Get this on as tight as you can because this is what creates a watertight seal on the cistern’s side. If this isn’t tight your toilet will leak even when it’s not flushing. It will just leak all the time. Tighten that up with a pair of grips. Some people put silicon on when they’re doing this bit if they’re not quite sure that they’re going to get a good seal. Get the doughnut and slip that over the top like that. Try and make it so it goes round the nut as well. So it sits on there. That’s a nice new doughnut. That will make a good seal. You get these here.

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