The Invade helps clean the drain where there is a scum build up. The Doxem NXT Aerosol will kill flies and stop the fly life cycle.  The whole idea here is to remove any food source where drain flies are breeding with these two products
Product Information
Invade Drain Fly Kit
How to Use Invade Drain Fly Kit
First use clear packing tape, with holes punched in the top and place over drain to see if there are drain flies coming out of the drain. Use clear tape so you can see thru it and punch holes in it for ventilation.
Use the Invade Bio Drain Gel to eliminate the source from the drains
Use the Doxem NXT Aerosol to treat drain flies as crack & crevice, void, or spot application
(A) 1 x 1 qt of Invade Bio Drain Treatment Apply 4 oz. to each drain around the edges to coat the sides. Repeat daily for 5-7 days and then every 1-2 weeks for ongoing maintenance. For drains that have a very heavy layer of scum, clean the drain with a brush before beginning treatment for immediate results and then maintain with Invade Bio Drain to prevent further build up.
( B )1 x 15 oz of Doxem NXT Aerosol The Doxem NXT has a broad-spectrum insecticide with four unique modes of action can be applied in entirely different ways than before with its flexible label.
Various applications: Crack & crevice, void, or spot applications
Use locations: May be sprayed indoor and outdoors.
Wide
label Use: Besides fly control usage,Doxem NXT may also be sprayed in food handling areas for German roach control and mattresses for bed bug control.