This is a very interesting question...
I have arrowroot powder in my pantry, based on previous references to it. I had never used it or tasted it before, but I just checked and it does have an anise-y flavor!
I found this reference
to tapioca/cassava flour, which indicates that less than 1/4 cup serving is allowed. I would guess a serving of something made in the slow cooker would contain way less than 1/4 cup. [ETA again: whoops, looks like this link is blocked. It's another SBD board. I summarized the gist of it]
Whole wheat flour might work? Or almond/peanut flour, depending on the recipe?
I just skimmed my two slow cooker cookbooks and they don't use thickeners at all. I would probably see how a recipe turned out without the thickener at all, then add tapioca flour or whatever to thicken it if needed. It should be a really small amount.
Oh and I just saw this list of substitutes
(ignore all the grammatical errors):
Substitute for Tapioca Flour
Before opting for tapioca flour substitute, you ought to know the quantity of the alternative that can substitute tapioca flour. The most common tapioca flour alternative is arrowroot powder. Corn starch, potato starch, kuzu powder, sago starch, sahlab, soy starch, sweet potato starch, sweet rice flour and water chestnut flour are other substitutes. These ingredients has a particular measurement which allows its application in tapioca flour substitute.
Other tapioca flour substitutes are almond flour, garbanzo bean flour and coconut flour. Tapioca flour renders food chewy and tasty. It is used for making white bread and French bread.
- 1 tablespoon of cornstarch or corn flour = 2 tablespoons of instant tapioca flour
- 1 tablespoon of potato starch or rice starch or flour = 2 tablespoons of instant tapioca flour
- 2 tablespoons of all purpose flour = 2 tablespoons of instant tapioca
- 1 tablespoon of Arrowroot = 2 tablespoons of instant tapioca flour