Some years ago I bought my present house as a new build - "all mod cons included" i.e. a fully fitted kitchen with appliances, as part of the developer's sales pitch. The 3/4 bed det. house enjoys the benefit of three {wash-down] WC's: one each for the en-suite, the family bathroom and the hall cloakroom. A step up for us as we managed in a chalet bungalow for eight years with just one loo, in the only bathroom, for all seven of us!
This new property has had a number of "issues" which were, to a greater or lesser extent - during the permitted 'snagging' period of 2 years, dealt with, usually quite promptly, by the builders; a.k.a. Developers.
The cloaks' WC, however, has never been "right" from day one, in spite of the plumber (and his mate), on contract to the builders, returning, at least half a dozen times, attempting to "fix" it.
They did eventually "solve" the problem, i.e. the flush did not work with a single cranking every time and mostly required to be cranked vigorously a number of times to get it to work at all.
However, being of an inquisitive disposition, I was moved to look more closely at what they had done and how they had "managed", after so many visits, to cure the fault. I discovered immediately that they had concocted their own design of linkage with non-standard bits and pieces - like something from a deranged Meccano set (point 1) and, instead of the quick change siphon, originally fitted, they had replaced the siphon with an earlier type 'cannibalized' (by their own admission) - of defeat? - from another unit. (point 2). Furthermore, this was the fourth siphon they had fitted: the three prior to this being the quick change version I mentioned above (point 3).
By this time I realised I was not going to get a better job done so I resigned myself to having to do the job myself. This necessitated having to remove the entire cistern from the bowl in order to detach the siphon; a job now largely eliminated by later designs of siphon.
I replaced the siphon with a Dudley Turbo SSR and also replaced the inlet valve - whilst I was at it - to a silent, turbo type: the one with the tiny float.
All well and good I thought. But no. Whilst the loo flushes almost without fail with just one crank of the lever and the wash down full and strong, the noise as it washes down is much greater than the two other identical units in bathroom and en-suite. It also nearly always requires two flushes to clear the bowl properly.
So, what could be wrong? One thing I can advise is that the sewer outlet pipe, which goes straight into the floor is offset, i.e. is not directly behind the [P trap] spigot on the bowl. This has necessitated the use of a flexible connection from this spigot to the sewer pipe which sits, virtually flush, in the floor. Could this 'arrangement' be the cause of the noisy flushing and the need to flush - most times - more than once?
If so, I can't see there being much I can do about it - short of digging up the floor and re-aligning the sewer pipe....or is there another way?