While cleaning the room with my plants in yesterday I found another slightly fun way to get rid of a fairly large amount of gnats. I used the hose attachment on the vacuum cleaner to suck them out the air, I noticed within a few seconds of knocking a pot that alot of gnats would come out the soil and start flying around, unfortunately for them it would be there last flight. You have to be careful not to get the vacuum hose to close to the plants or you will end up with some missing leaves, also not to close to the soil or you will start to lose that too. I think I got over 100 gnats in a few minutes. I will have another go today