For long term storage of aquatic insects I use 70-80% ETOH in glass screwtop vials with polycone/polyseal lids. I use 4 dram vials although I know lots of folks who use smaller (2-3dram) ones. There are other approaches (dry collections, shell vials, etc.) and preservatives (formalin, Isopropyl alcohol, Kahle's fluid, freezing, etc.). All of which are used for specific purposes. For a general collector who wishes to easily examine the collection I recommend screw top vial for ease of access to material and ETOH for general safety (safer fumes - although flammable). The polycone/polyseal vials, when correctly sealed, seldom lose fluid. The biggest problem seems to be a chip in the vial rim that does not allow a tight seal. I check my vials every year or so to see if any have lost any fluid - and replace the vial that has.
I recommend settling on a size/method up front as you can then standardize your vial storage system for ease of use. There are lots of dealers out there - search glass vials or entomological supply. You can also drop me a pm.
One of the most important items for a collection to be useful is proper collection information with the sample. A specimen without accurate collection data looses 95% of its value as far as I am concerned. At a minimum you need enough information so that someone is able to go back to that same place. At a minimum: State, County, indication of habitat (stream, lake, marsh, spring, light, spiderweb, etc.), detailed locality (eg. bob creek at bill road, four miles east of joe city), collector, and date. Some folks are now starting to use GPS info (I prefer digital lat/long) and it is a good addition but do not use it alone. A typo in a location can usually be deciphered - a typo in a lat/long cannot.
And, if you actually start to accumulate material for the long term please consider placing in a long term, well curated museum collection of aquatic insects once you are done using it. Too often such collections are simply tossed out and the value is lost.
may the collector gods be with you............
creno