Tom Del Rosso wrote:
"Jim Thompson" wrote
in message
Yep. When I was scouting out universities while I was still in high
school there was a demonstration at the University of Cincinnati of a
sewer mechanism to handle low flow neighborhoods.... a cistern filled
up with sewage and water until it reached a certain critical level,
then flushed itself... no moving parts.

How did it retain and release the sewage with no moving parts?

This is a common technique used in some septic tanks to give the drainage
field a break. The tank is broken into two chambers. The first chamber
holds the nasty stuff, and overflows into the second chamber. The second
chamber has a pipe that comes up from its bottom, and performs an upside
down "U" bend that goes back to the bottom (inlet). When the tank fills
enough to make the water fall over the top of the "U" bend, it forms a
siphon which draws all of the water out of the chamber.

In the case of a septic tank, the pipe that forms the "U" bend has to be
sized small enough that a toilet flush will cause it to fill completely
and start the siphon. This is not a problem, because the second chamber
has nothing but water in it. For a municipal sewage system, the bend would
have to be sized based on the usual usual flow surges that occur in the
sewer lines.

-Chuck