Had so many problems with air in my system that it's really been anoying me in fact it hasn't been right for years! I've got rid of every hoselock connector and have shares in ptfe tape manufacture. Whenever my tank dropped below half full i'd get an air lock. Had to be when the water sloshes about I thought.
Anyway yesterday I got to half a tank without moving the van and sure enough the problems start again - flow starts dropping, pump won't stop etc. finally my pole hose exploded whilst chatting to the custy.
It has to be the DI vessel!Got home and started all over again when I noticed a square plug on top of the head a bit like a sump plug on a cars axle. Took it out and taped up the threads and things have been fine ever since (I think

).