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.
A good home remedy for poison ivy is chlorox. It does no damage to the environment and is sometimes used to pour in well water to purify. You can spray it on at full strength or can mix with water to dilute and cover a larger area. Caution: it will kill other plants as well.