scrub the cage down with vingar and water or lemon juice and water if you don't like the vingar smell. and make sure to scrub both sides of the bars. the mixture is two parts water one part vingar or lemon juice. are you washing the bedding by hand or in washing machine. sometimes hand washing, if not done thoroughly enough will not get rid of all the smell. but there are people that prefer the hand wash method to make sure that there's no strong odours from the detergent. i use the washing machine personally nad just let the bedding sit out for a few days (often a week) before using that bedding in the cage. airs out any strong odours.
if the vingar and water mixture doesn't work (and i don't see why it shouldn't) you can also bleach clean the cage but i wouldn't do this unless you knew you could rinse every last trace of the bleach off. if you can take the cage out and hose it down afterwards maybe.
another method to get really stubborn odours out (i've never had to use this mind you, but have heard about it) is to take the cage to a do-it-yourself carwash and wash it there. i imagine it would be really easy to clean there with the high pressure water and all that (and i may try it this summer) but where i currently live its quite the trip to get to one. instead, in the summer i just use the garden hose and vingar and water in a spray bottle.
but perhaps the odour isn't being held in the cage bars. do you have plastic or wooden toys, hidy-holes, houses or igloos? if that's the case trash the wood. besides not really being able to tell what wood its made from the odours from them are impossible to get out. as for the plastic stuff send them through a round in the dishwasher. if you don't have a dishwasher wash them by hand in the sink.
you could also give your rats baths. i know there are some people that don't bother as rats are pretty good at keeping themselves clean but i find it makes a difference in the texture of their coat, the ammount of hair on their tails and their overall odour. it also helps keep the white or pale rats the right colors. i use baby (johnson's) shampoo. i've heard others use puppy or kitten shampoo but i'd be a bit concerned about the oils used in them. i know that if you use dog flea shampoo on cats you can kill the cat so i go with the mild baby shampoos instead. if its not going to harm the delicate skin of a newborn baby then its not going to harm the skin on the rat.
anotehr problem may bet that your litter isn't absorbig the smell enough. i find yesterdays news to be amoung the best at that. i've heard that corn cob litter is also popular for this reason. the wood (aspen-pine and cedar are a big no-no) litter i find doesn't do much for odour control. if you use the right bedding you can get away with only really havig to clean the cage once a week. and if you deep clean (scrub the heck out of it) at least once a month) you shouldn't ahve a problem with odours.
as a sort of related side note you could train your rats to use a litter pan in the cage. cleaning that is a lot easier then the whole cage (though bedding-cuddly towels and hammocks should still be changed at least once a week). all you have to do is empty it every so often (depending on the size of the litter box) instead of scrubbing quite so hard on everything once they have fully mastered the litter box. now, having said that, i have not myself trained a rat to use a litter box (i keep meaning to do it but something always comes up when i'm looking up methods) but have heard great things about it and its supposed to be really easy to do.
anyway, try those things and you shouldn't have any problems with odours.
