if you look at your radiators there should be a drain off valve either on the lock shield or near them on the pipe work.
If not a fella on here left some good advice about a self tapping drain off. I personally would not use them but the person who was left the advice said it worked a treat. so have a look at some of the other questions on here about draining a radiator.
i agree about the self cutting taps to drain off great idea but never leave it on ,replace it with a tee and a drain off,the boiler should have a drain off to release the pressure then use a rad to drain the rest if you dont fancy cutting in the system with the self cutting tap,why are you draining down ?
This is a common problem. Best way to do this without causing a mess is to get one of the DIY washing machine valve kits that cut into the pipework and make their own hole sealing around the pipe as it does so. This will have a shut off valve that can be attached to a normal washing machine supply hose, this can be turned on and off as required until drained down. Of course you will have to cut in a drain off but this can be done in place of the washing machine valve you have just used!!!Happy days!!!!! :D