My old 6m pole finally died but only ever used it twice a month so didnt want to splash out on new pole. So cut off top fitting of Harris 5m pole and inserted the brass male end of a drain rod drilled and tapped to take a 6mm bolt .Then took top section of a Harris 3m pole and fitted in the same way the female end of drain rod then the other end fitted another male end.
finally took a short bit of tube and fitted with female end and other end the conical fitting for brush.
pipework goes up pole as usual then have cable tied water tube to extension with a pipe connector.
just a case of screwing extension in for 6m or unscrewing for 5m and connecting up pipe .