Putting in the Grommet...I wonder if I am spelling that right? probably not.:
Depending on the length of your LED holders threaded shaft, and the overall thickness of your bucket, the grommet that you are using may not fit. THATS OK. If you cannot get your grommet into possition without being warped and wrinkled, or if you cannot get your nut and lock washer threaded on once you screw in your holder, then you need to use a razor blade to very precisely cut off one of the fluted ends of the grommet. The final product should look like a hollow mushroom.
Once you trim your grommet (it should still be hard to get in) use a scribe or a flathead screwdriver to gently coax the grommet into possition so that it is totally seated in the hole and there are no burrs pushing up the rubber.
The tiny shaft of rubber that used to bridge the gap between the two fluted ends of the grommet must still penetrate the bucket and be visible on the inside. Seen here from the inside with just a little bit of rubber showing.