Bit difficult to explain this, here goes:
I installed a new close coupled wc a couple of months ago. It has one of those push button flushing systems and, not that it will make much difference, it was made in the UAE.
The pan has the usual holes in the top rear shelf; there's the hole that the flush pipe goes into with the big rubber washer around it, two holes which allow for the passage of the filling pipe depending on which side you fill from although there's not actually a choice - it goes into the left hand side -and the other is just left vacant. There are also two smaller holes for the mounting screws which clamp the cistern and the pan together.
When the loo is flushed all is well until the last moment before the water stops flowing into the pan then, just as the water flow is cutting off, I get a spurt of water coming out of the vacanct fill pipe hole.
I can't see anything wrong with the rubber washer and the pan and cistern are clamped as tight as they can be without the dreaded 'pink' noise emanating as one of them fractures.
What's happening during the last moments of the flush to create enough pressure to blow water out of the joint between the pan and the cistern? Are we just looking at a replacement fat washer here and can you actually get them from merchants?
xav