Keep a bottle of distilled white vinegar in your bathroom cupboard. After brushing your teeth add one tablespoon of vinegar to a 250ml glass of water. Gargle, rinse around your teeth and gums and spit out as normal. Add clove powder or peppermint oil if you like to have a fresh feeling.
I actually keep my vinegar in one of these squeezy sauce bottle type doodahs, which I won a few months back (I think you can pick them up on eBay for about £3 for a double pack.) It keeps it sealed, the bottle is a bit slimmer so fits in my cupboard that bit easier than the glass bottle and I know that three hard squirts (cough) is roughly one tablespoon.