I have applied the product and there has been a decrease but not an eradication.
Expert response: Please note: Gentrol will not kill insects. Gentrol is a growth regulator so only nymph stages and eggs would be impacted by the application. It will take several months to see complete results from using this product. Please let us know if you have any questions, we are always happy to help!
Perhaps I didn't leave the mixture in the drains long enough before using then basins and shower, but it did not seem to work very well in controlling drain flies. I am going to reorder soon and treat the drains when we are going to be away from home for a day or two. Hopefully I'll get the desired results.