In such cases the weeps consist of small-diameter plastic, clay or metal pipes extending through the wall to a layer of porous backfill. Typically, weeps are arranged to direct water which may have entered an assembly from outside back to the outside.
A few of several safe household chemicals to use are vinegar, dishwashing soap and rubbing alcohol, according to an Oregon State University Extension Service publication called Using Home Remedies to Control Garden Pests, (EC 1586). The publication, complete with photos, is available free of charge online.
To use, mix 1 tablespoon with 1 litre of warm water and spray every bit of plant where you find the pests you're after. Oily pest control mixtures are best for mites, nematodes and hard shell insects, such as scale... it simply suffocates them.