20 gallon hexagon fish tank cycle and stocking?

i am getting a new 20 gallon hex fish tank in 5 weeks but i already have the filter i heard that you can put the filter in a container and cycle it like if it was the fish tank then just put the water and filter in the 20 gallon fish tank to speed up the cycle of the fish tank is that true and what fishes do you recommend for a 20 gallon hex tank thank you