More times than not the "hatch" the trout are feeding on during summer evenings on Montana rivers is a caddis returning flight. During the 12 years I lived in Montana, I found the most consistent and reliable way to catch trout feeding on caddis egg-laying flights was by fishing an elk hair caddis with intentional drag. Do this by casting downtream 45 degrees and put a downstream mend in the line to purposely induce a cross current drag. The most common caddis in Montana summers is the Hydropsyche, which is tan in color and imitated by a tan elk hair caddis on a #14 or #16 hook. The second most common caddis is imitated by a #16 olive bodied elk hair caddis. And when an elk hair caddis is fished with intentional cross stream drag, it stays afloat from the water tension on the wing stubb regardless whether it has floatant on it or not.
As far as household stuff to put on flies to help them float, Scotchguard water repellent is excellent. Spray some on the night before and a single false cast causes the water to leave the fly.