They have ways - I had a long talk with my plumber about this I asked him to install a Surrey Flange - see picture...
http://image1.betterbathrooms.com:81/betterbathrooms/6/5/6577e4fb1c8838bb482e8e7085c55f8b.jpg
...that stops natural air bubbles in the hot water tank going to the shower pump.
He refused and just put a T piece pointing downwards on an angled outlet pipe - said it did a better job at lower cost, see picture...
http://www.bathroomexpress.co.uk/images/techflow_turbo_installation_manual_fig4.jpg
It's only been a few months but no problems so far.
Pecavi, November 2008
