Having good luck with essential oil spray on a mowed-weed-style composting toilet. We separate
urine off, so it's a very dry situation. I can't vouch for whether this would work in a full-mixture CT. Maybe because this has some oil in the spray it is held in place by the dry weeds. I ran across this researching eucalyptus oil for insect/mice repellent, but any essential oil mixture could be used. We also have not had any gnats since we've separated off the urine.
In a 4 oz. spray bottle choose among favorite essential oils such as (get 50 drops total):
20+20+10 or 25+25, etc.
Step 1.
Eucalyptus oil (repels flies)
Lemongrass oil
Bergomot orange oil
Peppermint oil
Cinnamon
Vanilla
Rosemary
Sandalwood
.....etc....
Step 2. 2 tsps rubbing alcohol
Step 3. Fill the sprayer with
water
Shake, shake, shake! (shake before each use)
Spray on weeds or sawdust after each addition.
An important distinction: Permaculture is not the same kind of gardening as organic gardening.
Mediterranean climate hugel trenches, fabuluous clay soil high in nutrients, self-watering containers with hugel layers, keyhole composting with low hugel raised beds, thick Back to Eden Wood chips mulch (distinguished from Bark chips), using as many native plants as possible....all drought tolerant.