taking up on Roberts point
if you prespray and then agitate, what you are ensuring it that the prespray is getting around all the fibres so it can do its job of loosening the sticky dirt, then you can flush with the wand.
with the agitation of a Envirodri type of machine you can see the dirty areas "disappear" as you agitate. Its not really gone anywhere, just spread out more ready for the flush - but you know its been released from the fibres when it "disappears".
James - re the weight - 3 weetabix for breakfast. IWhen I had the Envirodri I used to put it at my side and straight lift it with th handle under my armpit, that way the weight is close to you and a straight lift.
With the Flexi 5/Carpetgard I now have, its a different shape and more weight (vac pod) and so it really does become a weight to carry. But if I can, you young wippersnappers can!