2nd floor washer drain pipe was misplaced in slab and moved during construction to be correctly placed within the wall that is between our dining room and the garage. However, concrete was not poured up against the pipe, and the remaining hole is about the size of my hand, and I can touch the rocks which are under the slab. Initially, a faint smell of mildew existed but no visible water damage. I opened up the wall on the garage side and easily cleaned up minimally damp drywall and mildew. Two plumbers looked at the problem and agreed upon a coupling to "fix the leak". I left the wall open and the pipe continued to sweat the exact same as before the coupling was installed. I noticed the sweating always is at and below the slab level and it was never related laundry frequency. Sweating does appear to be related to the amount of moisture in the ground, i.e. after rains and especially during cooler air temperatures. Also, the hole is warm and humid. Should I just pour concrete into the hole and up to the pipe to prevent the warm air from condensing with the colder air?