I use a 20l tubby Brabantia pedal bin with bio-bucket which lives in the kitchen. The Brabantia seems to manage our organic waste for a week. Another way of coping is to do a lot of the 'rough trimming' - leek leaves and roots, globe artichoke trimmings etc. - sat on the side of the compost bin down at the plot.
Like you, I live in a 3rd floor flat without lift :o I've tried oodles of solutions - if Brabantia stop selling this bin (it's not cheap) I will probably go for a nappy bucket with a biodegradable plastic bag inside. Tried the crock pot, gave it away as a pressie as it's far too small. But the Brabantia has been best solution I've found, used one for years, but I drove over the bucket in a mad moment :-\ and a chum is getting me one for a late Xmas pressie :D It doesn't smell because a) the lid is tight, and b) we've started layering with shredded office paper, that keeps it reasonably sweet inside. Cleaning the bin is best done at the allotment IMO :-X