Not sure what material the bucket lid is made of, but I will assume plastic.
I don't know the exact size of your grommet, but you can easily make the appropriate size by using a step-bit. Just go slow and easy, and you can check it as you go along to make sure you get the right size.
I did the same when enlarging the hole to accomodate for a temperature control grommet.
If you don't have a step bit, take your drill bits and select the one that is just slightly too large to fit cleanly through the hole in the grommet. When in doubt, drill too small, test fit, then step it up if needed.