Filter bed is good before the NFT, but don't leave it empty. put some plants in there!
If you find the bucket pre-filter involves too much work to clean, or needs cleaning so regularly it becomes a chore, you can make it into a swirl filter with a drain tap for easier cleaning
You can place a pipe in the center bottom of the filter, a ninety degree fitting attached to the outside of the container to this with an extension and finally a tap at the end for convenient/periodic draining.