Beetle juice and milk bambuckets are consumed upon use if there is only a single bucket in the stack, and no empty buckets in the inventory, and the inventory is full.
Beetle juice iron buckets simply can't be used. (cannot be drunk from but can contain fluids)
Beetle juice fails to kill attached bot fly larva.
Beetles don't seem to be milkable with iron buckets.

Betweenlands weedwood and syrmorite buckets have beetle juice bucket items that can't be used nor created via milking. (not this mods issue really, they can contain the fluid and be used with tanks)

working my way though quite a few bits - most of above is fixed - leaving open as other issues here are still present atm.

Closing for now as this should mostly be working as intended in the 1.0.20 update.