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CSLB trade exam · C-42 – Sanitation System
Pass the California Sanitation System (C-42) contractor exam.
Original practice questions weighted like the official CSLB outline, each with a plain-language explanation and the code or source behind the answer. In English and Spanish.
25 questions. No sign-up. A score for each of the 5 exam sections.
A first C-42 license takes two exams
The C-42 exam tests your trade; Law & Business is the same exam for every classification. You have 18 months from the day CSLB accepts your application to pass both. Already licensed and adding C-42? You take only the C-42 exam.
C-42 – Sanitation System
The trade exam for the C-42 Sanitation System license: planning and estimating sanitation systems, new septic system installation (tanks, leachlines and seepage pits, testing and grading, alternative treatment and specialty systems), sewer lateral installation and repair, septic system maintenance and repair, and safety.
Law & Business + Sanitation System on one pass: $129 instead of $158.
See plans and pricesWhat the C-42 exam covers
CSLB's study guide splits the Sanitation System exam into 5 sections. We weight practice the same way, so each section gets the share of your time it has on the exam.
- Closed book: no reference materials in the room
- Multiple choice, four answers, one best answer
- 3½ hours to finish, as for every CSLB exam
- CSLB does not publish the number of questions
- CSLB gives this exam in English only; our practice is in English and Spanish
Planning and Estimating27%Planning sanitation systems; estimating sanitation systems.
New Septic System Installation26%Installing septic tanks; installing leachlines and seepage pits; testing and grading over septic systems; installing alternative treatment systems; specialty sanitation systems.
Sewer Lateral Installation and Repair10%Installing sewer laterals; maintaining and repairing existing sewer systems.
Septic System Maintenance and Repair10%Troubleshooting existing septic systems; removing or repairing existing septic systems; maintaining existing septic systems.
Safety27%Employee training and safety; job site safety.
CSLB License Examination Study Guide, Sanitation System (C-42), form 13E-42 (03-2026), for examinations scheduled on or after June 1, 2023. CSLB notes that the percentages are approximate.
References CSLB lists for this exam
- 2025 California Plumbing Code (California Code of Regulations, Title 24), IAPMO
- A Builder's Guide to Wells and Septic Systems, McGraw-Hill Professional
- Pipe & Excavation Contracting, Craftsman Book Company
- Residential Onsite Wastewater Treatment Systems: An Operation and Maintenance Service Provider Program, Consortium of Institutes for Decentralized Wastewater Treatment
- Cal/OSHA General Industry, Construction and Electrical Safety Orders (California Code of Regulations, Title 8)
Time and format: CSLB Examination FAQ.
How we get you ready for it
680 practice questions across the 5 official sections, plus 211 flashcards, in English and Spanish.
Practice one section at a time
All 5 sections, each with its share of the exam next to it. Put your hours where they change your score.
Every answer shows its source
A plain-language explanation and the code section or reference it comes from, so you learn the rule, not just the letter.
Every mistake comes back to you
Questions you got wrong collect in one place and wait to be fixed, and each round starts with what you have not seen yet.
Full-length practice exams and a readiness score
About 115 questions against the official 3½-hour clock, weighted like the outline, and a clear signal for when you are ready to book. CSLB does not publish the exact number of questions.
Study on your phone between jobs, in English or Spanish, and install it on your home screen. Everything a pass includes.
Pay once: Sanitation System alone or with Law & Business
One payment, no subscription, no auto-renewal. Access opens the moment the payment clears.
Three months of full access: enough for most people to prepare and sit the exam.
Six months of access plus three study extras, listed on each card.
Best value
Law & Business + Sanitation System
Both exams
Everything a C-42 applicant has to pass
$129$169 one time
$158 separately · save $29$218 separately · save $49
- Both exam courses on one pass
- One payment, one sign-in
- Pass guarantee on each exam
180 days adds, for each exam
- Study plan built from your exam date
- Key numbers sheet: L&B deadlines and fees, Sanitation System figures
- Search across the question bank
- 6 months of access, room for a retake
One exam
Sanitation System
Passed Law & Business already, or adding C-42 to your license
$79$109 one time
- 680 questions, each with its source
- All 5 official sections, weighted like the CSLB outline
- 211 flashcards and timed practice exams
180 days adds
- Study plan built from your exam date
- Key numbers sheet: the figures of the C-42 exam, each with its source
- Search across the question bank
- 6 months of access, room for a retake
Only need Law & Business? It is $79 on its own. Refunds: full refund within 14 days if you have used no more than 50 questions and not started a timed mock exam. See our Refund Policy.
Pass guarantee on every exam: if you study with us and don't pass, we extend your access for free until your next attempt. The first 30 days take one click in your dashboard — no paperwork. How it works.
Questions about the C-42 exam
Something else? Email support@cacontractorexam.com and we reply within 2 business days.
Do I also need the Law & Business exam?
For a first license, almost certainly. CSLB requires the Law and Business exam from almost every applicant in addition to the trade exam, and you have 18 months from the day your application is accepted to pass both. Already licensed and adding C-42 to your license? Then you take only the trade exam. How the whole process works.
What does a C-42 – Sanitation System license let me do?
A sanitation system contractor fabricates and installs cesspools, septic tanks, storm drains, and other sewage disposal and drain structures. This classification includes the laying of cast-iron, steel, concrete, vitreous and non-vitreous pipe and any other hardware associated with these systems. Source: 16 CCR §832.42.
What is the format of the C-42 exam?
A closed-book, computer-based, multiple-choice exam at a PSI test center, with four choices per question and one best answer. There is no penalty for guessing, so answer every question. CSLB gives 3½ hours for each exam and does not publish how many questions the C-42 exam has.
Can I take the C-42 exam in Spanish?
No. CSLB gives the C-42 – Sanitation System exam in English only; it is not one of the exams offered in Spanish. Our practice material is in English and Spanish, so you can learn the material in Spanish and practice the questions in the English you will see on exam day. Taking the exams in Spanish.
What if I fail?
You can retake it after 21 calendar days, as long as you are inside your 18 months. If you studied with us, our pass guarantee extends your access for free until your next attempt. What happens after a fail.
Are these the real exam questions?
No. CSLB does not release its questions, and anyone claiming to sell them should be avoided. Our questions are original, written from the official outline and the codes and references CSLB lists for the exam.
Guides for C-42
How ready are you for the C-42 exam?
25 questions across the 5 sections, about 20 minutes, no sign-up.