How do I wash a bike indoors?
I never wash any of my bikes with water. Water, specially at high pressure out of a hose may get to places it shouldn't (i.e. bearings) and thus reduces the life expectancy of your bike. 

Personally, I don't have a lot of space inside, and this works perfectly fine:


let your bike dry completely
scrub off all bigger chunks of dirty with an old dry cloth
use a cleaning agent (ideally something like WD40) for stains that don't come off easily
degrease your chain, also using a bit of WD40 and some dry cloth
possibly remove wheels from frame if you really wanna get everything off
reassemble everything, grease movable parts using a little bit (!) of chain oil or thicker grease (i.e. motorex) if needed
most importantly: repeat regularely, so your bike never becomes too flithy