Here's another concoction from another BB using SSS:
10 oz. Vinegar
10 oz. Water
4 oz. Avon Skin So Soft
1 oz. Repel-XP
How I mix it:
In a half-gallon milk jug, I double the first three ingredients, and since the weather has been SO hot and humid, I triple the Repel-XP to 3 oz. I keep it stored in the milk jug and pour into a fly spray bottle as needed.
After spending tons of $$ in past years on literally gallons on the expensive fly sprays, I'm realizing quite a financial benefit to this homemade mix, plus it's a lot less chemicals being applied to my horses.
I bought a lot of 8 big (16.9 oz.) bottles of Skin So Soft on eBay, and with shipping, each bottle came out to less than $4.00 each. The Repel-XP is the most expensive ingredient, and a bottle goes a long way with this recipe.
I've had no adverse reactions on either of my horses, and it doesn't smell too bad either.