With internal parasites they have to ingest the DE, that's why you have to give it for such a long period of time.
I use pumpkin seeds for internal parasites (specifically worms), they work faster and more reliably for us than using De internally.
I use DE for the external insect pests
in the garden, and as an element of compost
for soil conditioning.
We also will occasionally use it on our foods (light sprinkle like it was salt) to make sure we get some silica in our systems, since it is important for certain nutrient uptake.
I know some people that use it far more than we do on Buzzard's Roost.
The bacteria of the gut actually break the silica of DE down so that they can use it for their needs.
These bacteria are then eaten by the fungi and from there it gets into the plant roots
Yes, wet DE is ineffective DE, it only works for desiccation when it is dry, internally it is more a source of silica.
If you want to see how it works when wet, get a piece of wood
and use it like it was a sanding medium, it will, when wet, put a nice polish on hardwoods, lots of elbow grease will be required.
I use it as a final polish for French polishing guitars, it works a lot like super fine pumice for that purpose.