Texas OSSF Installer II Certification Exam
Questions And Correct Answers With
Rationales 2026
1. Which of the following is the primary purpose of a septic tank in
an onsite sewage facility?
A. To distribute effluent evenly
B. To treat effluent to drinking water standards
C. To separate solids from liquids
D. To disinfect wastewater
The septic tank primarily separates solids from liquids, allowing
solids to settle and scum to rise, beginning the treatment
process.
2. What is the minimum liquid capacity of a septic tank for a typical
single-family home?
A. 500 gallons
B. 750 gallons
C. 1,000 gallons
D. 1,500 gallons
Texas rules generally require a minimum 1,000-gallon septic tank
for single-family dwellings to handle typical wastewater flow.
,3. How often should a septic tank generally be pumped to prevent
solids from entering the drainfield?
A. Every 6 months
B. Every 3–5 years
C. Every 10 years
D. Only when it backs up
Pumping every 3–5 years is standard to prevent solids from
clogging the soil absorption system.
4. What type of soil is most suitable for a conventional drainfield?
A. Sandy soil
B. Loamy soil
C. Clay soil
D. Rocky soil
Loamy soil provides good drainage and filtering capacity, making
it ideal for a drainfield.
5. What is the primary cause of premature failure in a soil absorption
system?
A. Overuse of disinfectants
B. Improper tank lid placement
C. Excessive solids in the drainfield
D. Low water usage
When solids enter the drainfield, they clog pores, leading to
system failure.
6. What is the minimum separation distance between a septic tank
and a private well in Texas?
A. 25 feet
B. 50 feet
, C. 100 feet
D. 200 feet
Texas regulations typically require at least 100 feet to prevent
contamination of the water supply.
7. Which of the following materials is commonly used for septic tank
construction?
A. Wood
B. Concrete
C. Aluminum
D. Glass
Concrete is durable, watertight, and commonly approved for
septic tank construction.
8. Which device is used to measure the flow rate into a septic tank
during testing?
A. Pressure gauge
B. Flow meter
C. Soil probe
D. pH meter
A flow meter is used to quantify wastewater entering the tank
for design and testing purposes.
9. What is the main function of the baffle in a septic tank?
A. To increase capacity
B. To aerate wastewater
C. To prevent solids from exiting the tank
D. To filter bacteria
Baffles direct flow and keep solids in the tank while allowing
effluent to exit.
Questions And Correct Answers With
Rationales 2026
1. Which of the following is the primary purpose of a septic tank in
an onsite sewage facility?
A. To distribute effluent evenly
B. To treat effluent to drinking water standards
C. To separate solids from liquids
D. To disinfect wastewater
The septic tank primarily separates solids from liquids, allowing
solids to settle and scum to rise, beginning the treatment
process.
2. What is the minimum liquid capacity of a septic tank for a typical
single-family home?
A. 500 gallons
B. 750 gallons
C. 1,000 gallons
D. 1,500 gallons
Texas rules generally require a minimum 1,000-gallon septic tank
for single-family dwellings to handle typical wastewater flow.
,3. How often should a septic tank generally be pumped to prevent
solids from entering the drainfield?
A. Every 6 months
B. Every 3–5 years
C. Every 10 years
D. Only when it backs up
Pumping every 3–5 years is standard to prevent solids from
clogging the soil absorption system.
4. What type of soil is most suitable for a conventional drainfield?
A. Sandy soil
B. Loamy soil
C. Clay soil
D. Rocky soil
Loamy soil provides good drainage and filtering capacity, making
it ideal for a drainfield.
5. What is the primary cause of premature failure in a soil absorption
system?
A. Overuse of disinfectants
B. Improper tank lid placement
C. Excessive solids in the drainfield
D. Low water usage
When solids enter the drainfield, they clog pores, leading to
system failure.
6. What is the minimum separation distance between a septic tank
and a private well in Texas?
A. 25 feet
B. 50 feet
, C. 100 feet
D. 200 feet
Texas regulations typically require at least 100 feet to prevent
contamination of the water supply.
7. Which of the following materials is commonly used for septic tank
construction?
A. Wood
B. Concrete
C. Aluminum
D. Glass
Concrete is durable, watertight, and commonly approved for
septic tank construction.
8. Which device is used to measure the flow rate into a septic tank
during testing?
A. Pressure gauge
B. Flow meter
C. Soil probe
D. pH meter
A flow meter is used to quantify wastewater entering the tank
for design and testing purposes.
9. What is the main function of the baffle in a septic tank?
A. To increase capacity
B. To aerate wastewater
C. To prevent solids from exiting the tank
D. To filter bacteria
Baffles direct flow and keep solids in the tank while allowing
effluent to exit.
