Froggie, I do that with plants I bring in from outside, too. Lots of pillbugs and sowbugs in the tub after. Yuck! But it works.

For gnats, I spray with a combo anti-fungal/anti-insect/anti-mite spray. The brand is Safer or something like that, and it contains neem oil among other things. It's a more natural product so it's not as toxic to humans. I spray the foliage and the soil.

After spraying, I sprinkle cinnamon over the soil, which is supposed to be an anti-fungal. Gnats usually spread fungus, so not only are they just annoying, they spread diseases among plants. You can also use a sharp sand or chick grit over the soil on your indoor plants. This prevents the gnats from laying eggs in the soil since it's too sharp to get to the soil. This will help prevent them from coming back but doesn't get rid of the ones flying around. Those will eventually die, though.

Good luck Jan,
gg