Persistent Drain Flies: Seal Drains, Rule Out Fungus Gnats, Check for Slime

Four-month drain fly battle: traps cleaned, gel used nightly, city sewer flushed. Still 3–4 flies daily. Expert clarified: drain flies don't carry human diseases (tropical relatives do, but not U.S. species).

Two similar flies: drain flies (breed in drain slime) and fungus gnats (breed in damp soil). If drains are truly clean, it may be fungus gnats from houseplants. Test: cover drains with wet rags overnight; move plants to a closed room. Whichever reduces flies reveals the source.

County Extension said black body = drain fly, but fungus gnats are also black. Visual ID with magnification is more reliable.