geoff wrote:
Can anyone give me a bleedingly obvious reason why two identical WCs with
maybe a metre difference in head are performing so differently?

The higher one seems to suck like a ... , and leaves only just enough
water to cover the "S" bend. The other one circulates and leaves a normal
amount of water in the pan

I don't actually want to get too involved (for obvious reasons0 but can
anyone give a few pointers as to why the first seems to have an over active syphon?





Is the stack properly vented? I would guess that the falling water from
the higher loo is capable of exerting a greater suction because the height
of the fall is greater than the lower one. In fact, if water is being
pulled below the trap level in the upper pan, the lower one may be causing
air to be drawn into the soil pipe via the upper pan.

Tim