You buy a basic in line tap for £7 odd quid and put it on the end of the reel hose. Cheap and it works ok, you will drag it about and its a pain reaching down for it. If you don't mind being tethered you can wear a holster as well.
Or spend a bit more and invest in either an aquadaptor or aquatap, I've used both but prefer the aquatap, more reliable, shorter and lighter. These fit to the top of the pole and brush screws to them, in the case of the aquadaptor a spung loaded mechanism is operated by pulling your pole hose to turn on/off the water. With the Aqua tap you twist the pole to operate it on and off
Darran