I didn't understand - it sounds like the problem isn't the dual flush but the use of a drop valve system, introduced in 2001.
It implies that dual flush doesn't require a drop valve system ("Most dual-flush toilets use a drop valve system" suggests that some do not.)
So was the "water-saving device" supposed to be the drop valve system? Because the main focus of the article is dual flush toilets, not drop valves.
I did a DDG search and found http://www.elementalsolutions.co.uk/wp-content/uploads/2012/... from 2012 which describes that leaky drop valves in dual flush toilets was already a known problem then.
It points out that one of the disadvantages to siphon flush ("all UK toilets prior to 2001") is "Dual flush operation less obvious to the user", so dual flush is certainly possible with siphon flush.
While it points out that one of the advantages of a drop value is "Allows lower flush volumes by giving a higher flow rate." Which makes it also a water-saving device.
Which makes me think the article has the wrong focus.
