Drill a 6mm hole in water butt lid, thread the inlet tube through, push filter on to end, adjust length of tube so filter hangs 10cm off bottom.
Take other end to pump, ensure there is some slack, cut clean and square and push onto inlet marked "I" so that tube is straight and does not pull.
For the "C" series models you also need to attach the water level sensor to the tube just above inlet filter and immerse it in the water. This will detect if the water barrel has run dry and will emit an audible warning. It also switches the unit off. This is supplied with 5m of cable - if you wish to mount the control unit further away from the water butt, either: