I use my wfp direct from the customer's outside taps for most conservatory work. And it's all you need for polycarbonate roofs.
Soap up first (I use tfr) and then rinse off. If you need to, finish off with a jet from the hose pipe to dislodge any twigs etc from under the ridge capping. (As an alternative, take the brush off the pole and wrap a cloth round the end. Then use it to get to the places where the brush won't go.
The brush also does the sides and gets rid of all the cobwebs and nasty bits easily.
Then just finish off the sides with a cloth and blade the glass as usual.
Fastest way of doing gutters, fascia, soffits ===>
http://www.youtube.com/watch?v=V9tRCCtCubIJob done.