I asked the exact same question of my independant mechanic who I've known since childhood.
He told me to get a good industrial degreaser, one that is suitable for all kinds of materials like rubber and plastic. Dilute it to the manufacturers recommendation.
Then go to the supermarket and buy a good selection of brushes, generally soft, but also a stiff one. I bought a dish brush, a bottle brush and a dustpan brush, plus a special wheel brush that's sort of hooped, a bit like a small toilet brush.
Soak the underside and the engine with the degreaser, then go to town with a bucket of water and the assorted brushes. I hose it off with a Karcher pressure washer, but take care to keep the nozzle far enough away so that it doesn't penetrate the water through the bearing seals and brakes etc. We have water restrictions, so a hose is not possible and against the law. The Karcher picks up water from a bucket and I can rinse the whole bike with two buckets, so it's water wise and legal.
I then dry it with a soft clean towel, spray WD-40 on the engine,wiping it off with a cloth and polish the paint with Nu-Finish (Google it) polymer sealant. The final process is a dusting and cleaning the screen and mirrors, which is always done with a Micro Fibre cloth.
Where I used to live I had access to a big old leaf blower, and a compressor, which makes the drying task easier. When I move again shortly, I'll be back to using these to do the drying.
A good 2 hours is all it takes for the above, so hopefully you'll find some of it useful.
One tip that a classic owner uses is to attach a sprayer with Kerosene in it to his compressor, then spray the whole bike with Kero at a reasonably high pressure, about the same as a garden hose. He then removes the gun and dries it with the air nozzle. His bikes always look brilliant! Watch the kero on the tyres though!
Mick
