Jul 23, 2014 - 08:23 AM
Most of the time, fruit flies are not a problem in drains. However fungus gnats, and phorid flies and drain flies can be a problem.
You need to be certain which fly you are dealing with, because they all originate from different sources.
To answer you question, Drain Gel is perfectly safe to be applied to PVC drain lines. It does not contain any harsh chemicals. In fact, it comes in a plastic bottle.
The bigger question is, does the septic system need treatment, and what kind of fly do you have? Here is our page on fruit flies with pictures - http://www.epestsupply.com/how_to_kil...