We order online from a store called "Do your own pest control" or some such. The drain fly gel works reasonably well; we use it weekly in the summer, and one or two stray ones seem to survive. I HATE HATE HATE them, but removing the offending pipe (under the concrete floor in our basement) is not in the budget right now.

Wow, I didn't know they made any. I have just poured beach or vinegar and flushed it really well with water. Do it a few days in a row and weekly flushes till the flies stop. I put a stocking over the drain so no flies would get through.

Is there a brick and mortar store at which to buy this? Or do I just need to order online? TIA.