Permit and Resource Management Department Banner

WLS-015 Procedure for Purging and Adjusting a Pressure Distribution Septic System

Revised 04/27/2006

A pressure distribution septic system consists of a network of small diameter piping in a system of lateral lines through which the wastewater is distributed by means of a hydraulic sump pump. These lateral lines can become clogged which adversely affects the equal distribution of wastewater in the septic system. To counter this, it is recommended that the lateral lines be purged and adjusted once a year for residential septic systems and twice a year for commercial septic systems.


Most pressure distribution systems have purge and adjusting valves placed at the beginning and end of each lateral line to manually purge and adjust the lateral lines. See diagram on next page. The following procedure, which is most efficiently implemented with two people, must be followed in order to properly purge and adjust a nonstandard septic system. Otherwise, a licensed septic system contractor, familiar with pressure distribution systems, should be contacted to make the adjustment.

Purging Lateral Lines

  1. Wear gloves, appropriate clothing and eye protection during this procedure. Wastewater is unsanitary and contains many pathogenic organisms which can be harmful to humans.
  2. Referring to the approved septic design plans, locate the valve box cover at the end of the first line, open the cover and expose the purge valve. Fully open the purge valve by aligning the handle parallel with the lateral line.
  3. One person presses or switches the “Pump On” or “Pump Activation” switch on most alarm boxes, (if you do not have a switch, contact a licensed septic system contractor). This manually activates the sump pump and wastewater should now flow through the distribution system pushing the suspended solids out of the lateral line through the open purge valve. It may be necessary to keep the switch depressed for up to a full minute to achieve a steady, clear flow through the line. The second person observes the flow until it runs clear and then informs the other person to stop the pump. If necessary, the adjusting valve, which is located at the beginning of the line, should be fully opened to achieve a flow rate sufficient to discharge water out of the end of the lateral line. Be sure to note the number of turns required to open the adjusting valve so that it can be returned to its original position after the process is completed.
  4. Fully close the purge valve so that the handle is aligned 90 degrees to the lateral line. Repeat steps 2 and 3 until each lateral line in the septic system has been purged. Make sure that all purge valves are fully closed when the process has been completed. If the wastewater does not flow easily through each of the lateral(s), a line is probably blocked and a licensed septic system contractor should be contacted for assistance in clearing any line blockage. 

Adjusting Lateral Lines

  1. If the septic system is so equipped, attach squirt fittings to the open end of the purge valve on the end of each lateral line. Fully open all purge valves to allow water to flow through all lateral lines simultaneously. If the fitting is located in front of the purge valve keep the purge valve closed (if not so equipped, contact a licensed septic system contractor familiar with nonstandard septic systems to install the fittings). Activate the pump manually as before but, in this case, balance the flow to each line by changing the settings of the adjusting valve(s) on each line to achieve an equal squirt height. Refer to the septic plans for the proper squirt height; if this is not indicated on the plans, a five (5) foot squirt height is typical. This is the most difficult part of the process and may require additional water in the sump to activate the pump while also adjusting the level of the water going to each line. It may be necessary to contact a licensed septic system contractor if equal distribution to all lateral lines cannot be achieved.
  2. After changing the adjusting valve(s) position to achieve equal distribution of the wastewater, fully close each purge valve. If the squirt fittings employing a drilled hole are located in front of the purge valve, replace these fittings with ones that do not have a hole in them.
  3. Change any soiled clothing and wash immediately to reduce the potential of exposure to any wastewater that you may have come in contact with during the procedure.