because when it passes thru a septic tank the enzimes and bacteria "work" on the waste water to clean it or break it down . when you go into the ground with out benifit of the septic tank you introduce chemicals and waste that are harder for the soil to clean. Most codes long ago in fact had a seperate system for the wash machine discharge thinking it over loaded the septic system. In most cases it was a distribution box and a few short runs . Experince has shown this was not a safe pratice for the enviroment. Here today homes have 2 and often 3 -1200 -1500 gal tanks in a row then a distribution box before going to the drain fiels . We have to get the tanks cleaned and inspected every 5 years in an effort to not deposit chemicals and waste in the soil only water.
my home has 2 -1200 gal tanks
