I've read the discussion and I'm currently trying to clean my Tower Bridge without disassembling it. Firstly, I put it in the bathtub and I sprayed some degreaser on it, I left it for a minute so that it could descale dust, and then I rinsed the (partially disassembled) Tower Bridge

with current water. Dust simply disappears, but as soon as everything dries, terrible water stains appear all around the studs, especially on baseplates and/or on large plates. My question is: how can water stains be removed, so that the pieces really look brand new? What's more, we have hard water here...

Sounds like you have a problem with limescale. I haven't had a problem with limescale on LEGO so I haven't tried any solutions, but conventional limescale removal sprays for cleaning kitchens and bathrooms should do it. Alternatively, clear distilled malt vinegar will work: the acetic acid will remove the limescale. After using the limescale remover/vinegar, you probably want to rinse the parts in distilled water. Before trying any of the above on your Tower Bridge, I would recreate the staining on some spare test pieces of LEGO, seeing what works to remove the stains and checking that the LEGO part isn't damaged.

do your final rinse in demineralised (or distilled if you're wealthy) water instead of the stuff out of the tap.

or add some water softener to a bucket of tap water - look for it where you get clothes washing detergents.

Final rinsing in soft water avoids stains...thanks for the precious advices

Hi, I bought a second hand minifig with cape and the cape is a bit dusty.

Can I wash it with normal soap and water?

Just add a comment here for the UK readers....

You cannot buy peroxide in the UK except in very small amounts for bleaching hair, it is a "controlled" substance here. Therefore I use white washing powder as it contains up to "30% peroxide". The enzyme washing powders have the advantage they digest off the crap - and ABS plastic is not affected by enzymes. Note that you should be careful with UK washing powder as it is very caustic (alkaline) but I have not seen a problem with washing stuff from ebay (euch !)

I use a laundry bag, you can buy sets of bags from various places, and these are nylon nets; and wash in a sink as I think the washing machine bashes the lego around quite a lot.

I dry the lego by spinning at 600rpm in the washing machine (2 laundry bags to balance things) - then use a fan to give a final dry.

I always wash lego from ebay - it is usually pretty nasty. Bricklink second hand lego is usually pre-wash (mine is ;) )

If it's really dirty, I just park a big plastic bin (not too big) infront of the TV fill with water, add dish soap, and scrub every part with a toothbrush. Dunk, and throw into a salad bowl filled with water. Then from there, they get rinsed off lightly in the sink and dry on towels that are on the washroom floor - I have a couple of extra washrooms, so I can afford to take up most of all of the washroom floor. Dry studs up and organize 2-3 days later.