YOu can buy caustic soda from DIY shops. Be careful with it when water is added, it gets very hot. Wear rubber gloves. Pour it carefully down the plug hole. Avoid the flat area of the plug hole if you can (caustic can cause it to discolour). Leave for about half an hour then pour boiling water down. This also works with a blockage.
Not sure about avoiding build up save declogging regularly to keep things from building up too much. I tend to use the Mr Muscle on which is great.
I tried caustic soda which is much more of a faff to use(as you have to mix it) - I'd definitely wear gloves if you try it as it made the skin on my hands a bit funny after I used it.
DO NOT POUR hot water on caustic soda as even contact with coldwater will cause it to boil. Even dilute caustic soda can permanently damage the eyes on contact. Wear goggles and rubber gloves. Try hot washing soda solution first as it is a lot safer.
Yes washing soda is what I meant jomifl..:) Sorry .
I always call it soda crystals . I just put it down the sink and then put a kettle of hot water down .