Bonnet cleaning steps

someone says you clean them by hand?

There is a small oscillating unit made by the Oreck vacuum company that works. Most pad cleaners we do business with prefer to steam extract stairs and the cheap'o's use a bonnet hand mitt. Pick your category.

P.S.
Make sure you distinguish between synthetic bonnet and cotton pads. There is a big difference in actual soil removal.

If you seriously encap and want to do stairs with the minimum of fuss (or upholstery for that matter) then look up "Cyclo" - a twin brush orbital machine, hand-held, that makes doing stairs a breeze. Normally used in the vehicle detailing industry, but translates beautifully into our industry.

For stairs or in particular microfibre upholstery, nothing else comes near it!

try the chicago rotary tool.  Wipe with a cloth first.

If you want a cheaper, yet still extremely effective option, try a 1/3 sheet finishing sander with a microfibre mop cloth. Makita make ones with a nice spring clamp to hold cloths on, and they work a treat particularly on steps. The fact that they're rectangular in shape also means you can get right into corners, so that you don't have to hand detail them.

I've already tried that method.  Microfiber is great! It cleans well and absorbs well also.  The problem... Dirty Dirty Stairs.  When I'm cleaning the stairs I burn out the micro fiber towel or mop cloth however.  The best way is to use a rotary tool like the one's mentioned above.  But use a microfiber towel or regular terry towel to wipe the stairs clean as possible. 

Next step is to use a upholstery bonnet pad cut it in half and place it to a velcro strip on the rotary tool. Then Clean until your heart's content!

Hope I helped.  Just my two cents!