It's all co-ordinated by the sink frogs I tell you.
It is not ascertained just how many sink frogs live in the stmh pipes, but they can often be heard gurgling and burping. It is understood that these amphibious miracles are responsible for the delivery of water to and from the sinks.
[edit] June 2005
Our froggy friends seem to have moved out in protest at MrT's vomit deposits, leaving our plumbing unmanned.
[edit] 3 weeks later
Still no frogs, time to buy a plunger
[edit] Next Day
http://news.bbc.co.uk/1/hi/wales/4623893.stm
<Mr_T> did the trick though, the frogs are back!