How to remove tea and coffee stain build up on your cups and mugs

Pour a tablespoon of soda crystals into the bottom the offending cup and pour hot water to cover the cup stains completely. Leave to soak while you do something else for an hour.  
Rinse the cup and with the rough side of the sponge scourer the stains will just wipe away. Be sure to rinse out the soda crystal mixture thoroughly.