The fleas are attracted to the light and jump on the plate. Without the dish soap the water surface tension is enough that they can jump off but with the soap the sink and drown. If this is done for several nights eventually all the fleas will be gone unless more are brought in. Joanne Words From Experience Fleas are dangerous pests. They continue sucking blood even when full, because their larva feed on the blood that they pass with their stool.
Fleas carry tapeworms, and a bad infestation can cause serious loss of blood.
Puppies and kittens can die from flea caused anemia. Any insecticide you use will be absorbed through your skin and the animal's skin, and be breathed by you, the kids, and the animal. Our San Diego fleas are resistant to most insecticides. The ones that work are either really strong or act as hormones, with unknown long term effects on people. The following has worked for us for the past 10 years, and we have three large outdoor dogs and an outdoor cat.