What Is a Grease Trap and Do You Need One?
A grease trap (also called a grease interceptor) is a plumbing device that captures fats, oils, and grease (FOG) before they enter the sewer system, where they solidify and cause blockages. Grease traps are required by code for commercial kitchens and food service businesses. Residential homes don't typically need one, but homeowners who cook frequently with oils or have recurring kitchen drain clogs can benefit from a small under-sink grease trap ($50–$200). Commercial grease traps cost $500–$5,000 installed and must be cleaned every 1–3 months. Neglecting a grease trap leads to sewer backups, code violations, and fines up to $10,000+ in many municipalities.
Cost Breakdown
| Service | Low | High | Notes |
|---|---|---|---|
| Under-sink grease trap (residential/small commercial) | $50 | $500 | Unit cost; 8–40 gallon capacity |
| Under-sink installation | $100 | $300 | Professional plumber installation |
| In-ground grease interceptor (installed) | $2,000 | $10,000 | 500–2,500 gallon; excavation included |
| Professional grease trap pumping | $200 | $500 | Per visit; every 1–3 months for commercial |
How a Grease Trap Works
Grease traps use a simple principle: fats and oils float, solids sink, and relatively clean water flows through the middle. Wastewater from kitchen sinks and dishwashers enters the trap, slows down in a baffled chamber, and separates. Grease rises to the top and is retained behind baffles. Food solids settle to the bottom. The clarified water in the middle exits to the sewer line. Over time, the retained grease accumulates and must be pumped out.
Types of Grease Traps
Under-Sink (Point-of-Use) Traps
Small units (8–40 gallons) installed under the kitchen sink. Suitable for low-volume applications — small restaurants, food trucks, and residential kitchens. Cost: $50–$500 for the unit plus $100–$300 for installation. Must be cleaned every 2–4 weeks depending on cooking volume.
In-Ground Grease Interceptors
Large concrete or fiberglass tanks (500–2,500 gallons) buried outside the building. Required for high-volume commercial kitchens — full-service restaurants, cafeterias, and food processing facilities. Cost: $2,000–$10,000 installed. Pumped by a licensed hauler every 1–3 months. These handle much larger volumes and provide longer intervals between cleanings.
Automatic Grease Recovery Units
Mechanical units that skim and remove grease automatically on a timer. Higher upfront cost ($2,000–$7,000) but lower ongoing maintenance. Popular in high-volume kitchens where manual cleaning is impractical.
Do You Need a Grease Trap?
Required By Code
- Restaurants and commercial food service — virtually all municipalities require grease traps or interceptors
- Food trucks and mobile food operations — many jurisdictions now require portable grease traps
- Commercial buildings with kitchen facilities — cafeterias, break rooms with cooking equipment
Recommended but Not Required
- Residential kitchens with frequent grease-heavy cooking
- Homes with recurring kitchen drain clogs
- Homes on septic systems — grease disrupts the bacterial balance in septic tanks
Maintenance and Cleaning
A grease trap must be cleaned when the grease layer reaches 25% of the trap's capacity — this is both the industry standard and a common code requirement. For most commercial kitchens, this means pumping every 1–3 months. Neglected grease traps cause sewer line blockages, foul odors, pest attraction, and code violations.
- Under-sink traps — can be cleaned manually by scooping grease into a sealed container for disposal. Takes 15–30 minutes
- In-ground interceptors — require a licensed grease hauler with a pump truck. Pumping costs $200–$500 per visit
- Keep records — most municipalities require documented cleaning logs for commercial grease traps
When to Call a Plumber
Call a plumber for installation of any grease trap ($100–$300 for under-sink; $2,000+ for in-ground). Also call if your kitchen drains are slow despite regular cleaning — grease may have accumulated in the drain line downstream of the trap, requiring professional jetting ($200–$500).
Related Questions
What happens if you don't clean a grease trap?
Grease overflows into the sewer line, causing blockages that back up into the building. For commercial kitchens, this also triggers health department violations and municipal fines — often $1,000–$10,000 per violation. The smell alone from a neglected trap will drive away customers.
Can I put a grease trap on my home kitchen sink?
Yes — small under-sink grease traps designed for residential use cost $50–$200 and fit under a standard kitchen sink. They're especially helpful if you cook frequently with oils or have a garbage disposal (which sends more FOG into the drain). You'll need to clean them every 2–4 weeks.
Do garbage disposals replace the need for a grease trap?
No — garbage disposals grind food but do nothing to capture grease. In fact, running grease through a disposal emulsifies it temporarily, allowing it to travel further into the drain line before solidifying. This makes blockages harder to reach. Commercial kitchens with disposals need grease traps even more.