Smelly basement drain...best way to clean it?

No need to over complicate things. Mix a 1/2 cup of baking soda with some warm water and run it down the drain. If this doesn't work then simple bleach can also do the trick, however you then have to deal with the bleach smell for a bit. On a side note, smelly drains can often be an indicator of larger plumbing problems. Are you experiencing slow draining sinks or showers anywhere in your house?

The smell is sewer gas. The drain has a trap shaped like a “U” that is full of water, when the water evaporates it allows the gas to pass. Pouring a few cups of water into the drain will fill the trap and stop the smell. Some people pour a cup of vegetable oil into unused drains because the oil will not evaporate. A unused toilet can do the same thing.

I always just dumped some baking soda down the drain and a little vinegar. Let it sit for a while and then pour some hot water down the drain.