Drain Fly Follow-Up: Leaky Toilet Seal May Have Been the Source

After a plumber cleared a drain and resealed a slow leak at a toilet base, drain fly numbers dropped sharply. The expert noted: a leak alone doesn't breed drain flies—but if it fosters algal/slime growth in the subfloor or wall void, that organic film becomes a breeding site.

Continue the bacterial drain gel treatments. If flies reappear, capture a few for ID via the county Cooperative Extension office to confirm the source.