Septic Systems (also called On-Site Sewage Facilities) have their own set of rules and requirements which are administered by the Texas Commission On Environmental Quality. Because these systems can create a safety and environmental hazard, special rules and processes must be followed.
The TCEQ has their own system of licensing and regulation - issuing licenses like Site Evaluator, Installer I, Installer II, and Maintenance Technician. All of these require their own set of prerequisites, education, and testing.
Many plumbing companies in rural areas of Texas have these septic system licenses and work on both the house’s plumbing systems and the onsite septic systems.