We recommend using a bowl and whisk to mix our products. Why? If you whisk it enough, you will create a foam, or meringue, which can be easily brushed onto the pet with minimal amount going down the drain.
What you are doing on a scientific level is, by mixing the shampoo and water, you are breaking down the globules of soap which increases the surface area of the soap which, in turn, increases the amount of dirt the soap will grab. Furthermore, if you leave the product on for 5 minutes, that increase the amount of time the soap has to grab even more dirt. Anything short of this process just makes your product less efficient and increases waste.