Not sure of the name of the pump, but I've attached a pic of it here together with one of the tank. Note the little "sump" - itself baffled in the foot of the tank.
I'm suspect some kind of flow meter is the only answer although even that won't stop the intermittent "tank empty" signals.
Any advice welcome.
http://www.aquamist.co.uk/vbulletin/...1&d=1296553380
http://www.aquamist.co.uk/vbulletin/...1&d=1296553380