We recommend using
Gentrol Aerosol to aid in treating Drain Flies. We like it because it comes with an applicator straw that eases application to hard to reach areas in and around sinks, toilets, etc. You can also use Gentrol Igr Concentrate, mixed with Suspend to treat areas such as your attic and crawlspace. Please make sure that there are no further water leaks, that could condusive to Drain Flies.