The wastewater now known as effluent, exits the septic tank through the rear baffle and travels through a solid pipe to the drainfield or drywell. If the system has more than one drainfield or drywell, it will have a distribution box. Drainfields and drywells are excavated and filled with stone and perforated pipe to distribute the effluent. The size and shape of the system varies and is determined by the local health department using information gathered from a perc test and is designed to handle the flow from the house and protect the environment.