As a comment I would suggest you slide the lifting arm forwards so it exerts a direct lift upwards and doesn't strain stuff. Some water will remain as once the siphon draws air in the column of water will collapse back into the cistern.
The ones I've seen in B&Q etc are intended to be cut to size - use the old one as a template - though TBH any bit of relatively heavy polythene sheeting will do just as well as a purpose-bought item.
Can't really see from the photo, but that sounds a bit more than 'normal' - you sure you aren't flushing in 'eco' mode or something?
Indeed. The lifting arm should give a straight lift. Why is it located right at the end of the 'shaft'? It isn't, by any chance, that the rod which pulls up the diaphragm was too long and, with the lifting arm correctly positioned, doesn't lift the diaphragm high enough? If so, shorten the rod (somehow).
However.... Once you've got the siphoning action started, it should keep going until air gets in - which should be when water level in the cistern is almost zero. If there are still 3 or 4 inches of water left, is air getting in to the works and 'killing' the siphon prematurely? Maybe there's a split in the cylinder or the inverted U-bend (especially at the top)?
Ours failed about a year ago at an inoportune time (visitors & shops shut). I cut a piece out of a polythene sow nut sack - actually I think I made it two layers. Still working now so not re-visited it!
Aha I found a hole low down on the side of the syphon. I pressed my finger over the hole and flushed and a lot more water flushed away. I will plug this with whatever I can find short term and asses if I get an improvement, then get a proper plug for it. I think there is only one bung hole, difficult to see properly.
Sounds and looks a bit like mine. Removing the bung puts it into dual flush mode. For a full flush hold down the lever - this causes a piston to cover the hole and it gives a full flush.
I`ll play around with that in the next few days in the meantime I emptied the cistern, dried off the syphon and just used a piece of gaffa tape over the hole, it should hold for a few days until I get a proper bung. Its now giving a higher volume flush.
Nonsense. Most syphons you buy are dual flush. The size of the small flush is adjusted by blocking/unblocking a series of holes with plug(s) provided.
I did read it somewhere - this type was criticised as people often found they had to flush twice to get the desired result because they didn't know of the "Hold Down for Big Job Flush" feature. Water savings were negated by people flushing twice. Modern types get round simpletons with two buttons.
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