Delta Dust Insecticide is not labeled for bathroom or kitchen drains, it is primarily for uee in cracks and crevice. If you have vents that blow air into the home caution should be used to take care the dust is not blown through the vents. Delta dust can be used on floor drains (to sewers).
While we cannot comment specifically on another person's application, it's not illegal to apply Delta Dust Insecticide in the rain. Delta Dust Insecticide is waterproof. Our concern is that if the rain storm was bad enough, it could potentially wash the product away.
Yes, Delta Dust can be applied to the base of the rock wall to protect against scorpions. This product is water-resistant and will not wash away in the rain if applied into the cracks and crevices. Be sure to re-apply every seven months.
Yes, Delta Dust Insecticide is labeled to be used along and behind baseboards, to window and door frames, corners, pipes, storage locations, attics, crawl spaces, garbage rooms, lavatories, floor drains (to sewers), entries and vestibules, offices, locker rooms, machine rooms, boiler rooms, mop closets and other areas which these pests may enter or crawl.
Delta Dust Insecticide is actually the most recommended dust for cicada killer wasps holes as it is 100% waterproof so will still work when wet.