Warning... I'm about to have a little rant about the MTR by-laws, vis-a-vis bicycle front wheel removal.
I see eye-to-eye on Martin Turner (over at
HK Cycling Alliance
) on the "requirement" of front wheel removal by the MTRC is not only an inconvenience... it is actually also
more dangerous than having a complete bicycle within the station, if only for the fact at least one hand would be free (both hands are used when one has to hold a bike, and another the wheel), the brakes work and there are no pointy (fork ends) or sharp (brake rotors) bits to cut and/or injure people with a bicycle that still has its front wheel attached.
On the last few times I've taken my full-sized commuter bike on the MTR (West Rail then Tung Chung line), I've gone through with the bicycle in one piece... curiously wasn't stopped at any point.
Anyway... if you do get stopped, Mr. Turner suggests you should explain to the MTR staff the above that a complete bicycle is safer to yourself and other passengers, with the bicycle in one piece, as opposed to partly disassembled weighty metal. If they start being belligerent, and you have time, ask for the station manager.
As for bike cleanliness... if you're coming out via Ho Pui, there's a store "behind" the village hall which has a hose-pipe that can be borrowed to rinse off the bikes. The downhill guys whom use the vans for shuttle runs make use of the store's hosepipe quite often when the weather is crap, as the van drivers don't like their vans getting all muddy... even more so than what the MTRC might be!