This is an easy one to do and quite satisfying, if a little stomach curdling on occasions!
Pouring fat down the plug hole is a quick way to block pipes and sewers. Rats are attracted to the fat too so it’s a quick way to encourage them to a drain near you!
Instead pour the fat into a fat trap and dispose of the fat in your bin. The original fat trap is reusable but there’s also a disposable paper version too. Alternatively fill a yogurt pot or margarine tub.
Fat traps are available from Less Mess or free from your local water authority.