Cooking oil and fat should not be poured down sinks as it can cause blockages.
Contact your local council to see if they accept it at the local recycling centre, they may even know of local organisations who collect cooking oil for conversion to bio fuel.
Tip: Google – ‘cooking oil recycling Wales’ to find out who operates a service near you.
Alternatively for small amounts (works the best with solid fat such bacon/lamb/beef/pork but not liquid oil), why not mix it with bird seed in an empty yoghurt pot, add a small stick with string attached and put it in the fridge to solidify. You can then hang it from a tree in your garden and feed the birds in the winter.