Hi Vince

I assume you dont mean how much goes through but what governs the final
level? More water is used to flush than just maintains that..

I'll admit I havent torn a US dunny to pieces just yet...

An Australian one however is set by the height of the exit pipe. The
entire pipe configuration is usually an "S" shape on its side (thats why
they call it the S bend...) such that if you pour water in one of the
upward facing holes it maintains the same level in the system by letting
excess go out the downward facing hole. ie the geometry of the porcelein
construction.

Varying heights is always associated with air pressure in the downstream
waste line, either permanently or temporarily. The main reason for a
sewer vent is in fact to keep the pressure the same as atmospheric.
You'll also find that geometry and fall height from other services in
your area can lower pressure temporarily and thus pull the level down. I
had a really stinky situation once where I was on the end of a 40ft fall
from above. It use to drag so much water from the toilet when they
emptied their bath that it left an air gap and the sewer smell entered
the house. It was resolved by placing an sewer vent just downstream of
my toilet.

The only way to get the "inward" level higher is to raise some part of
the exit pipe higher. That can be easy or difficult depending on its
construction. The simplest being to build up the lower pipe level with
some concrete. You might get blockages more easily though..

Cheers Bob


Vince wrote:

What component, if any, is used to adjust the amount of water that is
routed to the bowl ?