Most diaper pails have a place for a deodorant disk in the lid. You can make those disks yourself.
You will need:
distilled or boiled water
baking soda
your choice of essential oils
a muffin pan
paper muffin cups
Add a few drops of essential oil to a small amount of water. Mix the water with 2 cups of baking soda. Mix well. Gradually add and mix more water until you have a thick paste. Press about ½" of paste into each muffin paper and let dry 24 hours. Tear the paper off. After you've used each disk for a month or so (however long you find it effective), crumble the disk into the diaper wash. Baking soda deodorizes and softens the diapers.