My dd was a horror, 16 now and much better. I resorted to the binbag trick on several occasions, including iPads, kindles and phones (which I kept and she had to earn back, everything else was binned), but her room was still a pit. I tried to ignore it, if she wanted to live in that mess, get on with it. One day I went in and her ensuite toilet was completely blocked (almost overflowing, really) and knickers with used sani pads all over the floor and bed. Her room STANK. Plus the crockery, glasses, mugs, yoghurt pots - vile. It was truly a biohazard.
She was away for the weekend so I packed all of her stuff in boxes except school books, and moved her furniture and everything into the teensiest box room in the house (my office), with her boxes of stuff under her bed. Also meant she lost her sky box and tv.
She stayed there 6 months (was a couple if years ago now) and kept the room clean. Then she got her old room back and is tidy now - quite house proud in fact!!
It also amazes me how long it takes her and dsd to load the dishwasher which is their only chore. Can take them an hour after a standard evening family meal. Took me and DH about 3 minutes last Sunday to clear table, load dishwasher, wash up roasting pans etc (roast dinner), dry them up and put away, wipe table, hob and work surfaces, and leave the kitchen clean and tidy. 
They also tend to do their own washing as otherwise dh does it, and their stuff keeps going missing, he just cannot tell the difference between their stuff and mine so their tops and knickers often end up in with my stuff and vice versa and it drives them mad. It's a mans logic of 'do the job badly and you won't be expected to do it again' - it doesn't work with me but has trained the 2girls pretty well!