Welcome to the vinegar lovers club. I get white vinegar exclusively for cleaning (for consumption, I get wine vinegars, and Bragg's ACV--stock up when it goes on sale). The HDPE containers most of it comes in are fine for just about any food or chemical storage, as well.
For cases where you need serious cleaning, though, get one of the not-owned-by-megacorps brands on orange cleaner, and only get it concentrated (Orange Plus and Orange TKO are what I've used, but there are others just as good, I'm sure). A bottle will last a few years, and work magic. The likes of Orange Clean and Orange Glo have long since sold their souls, and are no better than the other crap on the shelf.
Drain... flies? Ewww, i've never heard of that before
I get them in my bathroom during the summer and fall. Since I began using real soap, they've nearly disappeared (next step: disassembly and cleaning of the sink and its drain, in the hopes of complete eradication). Supposedly they can't breed in oil, and leaving a layer of oil in the trap is one way used to get rid of them (which could be what my soap is doing).