Can You Flush Used Cooking Oil Down the Toilet? advises against flushing used cooking oil down the toilet. This method of disposing of cooking oil is likely to clog the plumbing in the bathroom.

A To Z Plumbing & Drain Service notes that cooking oil may be liquid when it is first dumped into a toilet, but it solidifies when it cools down. People who attempt to mitigate this problem by pouring hot water in with the cooking oil only cause it to get a little further down the drain before it solidifies.

Before disposing of cooking oil, wait for it to cool down completely. Pour it into a container with a lid or a screw cap; make sure that the container does not allow the oil to seep through. Close the container tightly, and dispose of it in your regular garbage.