Can a dishwasher drain into a grease trap in Seattle?

Not into a hydromechanical grease interceptor. Dishwashers, warewashers, and glasswashers must drain straight to the sanitary sewer. Public Health can allow them to drain to a gravity interceptor with an approved alternate means request.

Who issues the grease interceptor permit in Seattle?

Public Health Seattle and King County issues the plumbing permit that covers the grease interceptor. Side sewer work outside the building is permitted by Seattle Public Utilities.

How often does a grease trap need to be cleaned in Seattle?

Seattle's rule is based on how full it is, not a calendar: clean it before grease and food solids take up 25% of the interceptor. Busy kitchens may hit that in weeks.

Seattle grease trap requirements for restaurants: sizing, permits, cost

Q: Does a coffee shop in Seattle need a grease trap?

Usually, yes. Public Health requires a grease interceptor wherever food or drink containing fats, oils, or grease is prepared or served, and espresso machine drains and dipper wells are on its list of drains that must connect to one.

Do you need one?

Almost certainly. Public Health Seattle and King County's plumbing rules say a grease interceptor is required wherever food or drink containing fats, oils, or grease is cooked, prepared, or served. That covers restaurants, bars, bakeries, delis, and most coffee shops. Seattle Public Utilities puts it simply: if you have commercial kitchen plumbing and need a food service permit, you most likely need one, and Public Health will require it for new or remodeled restaurants that apply for a plumbing permit.

Public Health can make exceptions for places with no onsite cooking, such as warming kitchens, catering kitchens, and concession stands, and for existing fixtures that were in use before a remodel. Those are decided case by case.

Which drains must connect

Must drain through the interceptor	Does not need to
3-compartment sinks	Hand sinks
Prep sinks and dump sinks	Ice machine drains
Floor drains and mop sinks in the kitchen	Condensate drains
Floor sinks	Backflow preventer (RPBA) relief drains
Dipper wells and espresso machine drains	Other clear-water waste

Two common mistakes:

Dishwashers, warewashers, and glasswashers may not drain into a hydromechanical interceptor. They go straight to the sanitary sewer, or to a gravity interceptor if Public Health approves an alternate means request.
Food waste disposers and scrappers can't drain into a hydromechanical interceptor unless it is listed for solids or a solids interceptor comes first.

The two kinds, and how they are sized

Hydromechanical grease interceptors are the smaller units, usually under a sink or in the floor. They are sized by flow rate: the total gallon capacity of the fixtures draining to it can't be more than 2.5 times the interceptor's rated gallons per minute. For example, 60 gallons of sink capacity needs a unit rated for at least 24 gallons per minute.
Gravity grease interceptors are large tanks, often underground or outside. Public Health says to size them under the plumbing code and the manufacturer's instructions.

You may read online that King County requires a 1,000-gallon tank for every new restaurant. We found no such rule in Public Health's or Seattle Public Utilities' documents. Your plumbing designer sizes the unit, and Public Health checks it.

If you want to hang a hydromechanical unit from the ceiling or wall in Seattle, you need approval from Seattle's Fats, Oils and Grease program first ([email protected]), and proof of it must be on site at every plumbing inspection.

Permits and plan review

Plumbing permit from Public Health, not SDCI. It covers the interceptor and the fixtures. A brand new food space (a new building, or a space that has never held a food business) needs full plumbing plan review. Remodels and new owners at an existing restaurant usually get field review instead.
Food and facilities plan review, also from Public Health, is a separate process for your kitchen layout and equipment. It must be approved before construction starts, and the first review can take up to 8 to 10 weeks right now. The 2026 fees are a $1,008 base for new construction (covers 4 hours) or $756 for a remodel (covers 3 hours), plus $252 per hour after that.
Side sewer permit from Seattle Public Utilities if the work reaches the pipe outside your building. This moved from SDCI to SPU on October 1, 2025. You still apply through the Seattle Services Portal.

What it costs

Seattle Public Utilities says simple installations start at $3,000 and can cost a lot more when the job is complex. Outside estimates, which are not Seattle-specific, put a fully installed 1,000 to 1,500 gallon underground gravity interceptor at $14,000 to $25,000, most of it excavation and site work, and a typical pumping visit at $300 to $600. Get two or three local quotes before you commit to a layout.

Keeping it clean

The 25% rule. Under Seattle Municipal Code 21.16.310, an interceptor is in violation once grease, solids, or food waste take up more than 25% of any chamber, unless the manufacturer's written specs set a different standard. The rule is based on how full it is, not a calendar, so a busy kitchen may need pumping every few weeks.
No enzymes or additives. The same code bans emulsifiers, enzymes, and bio-additives in grease interceptors. They push grease further down the line.
The stakes. Seattle Public Utilities warns that a business without a working interceptor can be held responsible for sewer overflow damage to its own and others' property, city fines when an overflow reaches waterways, and closure over the health risk.

Who does the work

Seattle Public Utilities keeps a list of 26 companies that install interceptors, pump and maintain them, recycle grease, and clean side sewers, with the languages each one supports. The city notes the list is not an endorsement and is not complete.

Unlike kitchen hoods, grease interceptors don't show up in Seattle's open permit data, because the plumbing permit comes from Public Health. So we can't rank installers by permit count the way we can for hood and fire suppression contractors.

Common questions

Does a coffee shop in Seattle need a grease trap? Usually, yes. Espresso machine drains and dipper wells are on Public Health's list of drains that must connect to one.

Can a dishwasher drain into a grease trap? Not into a hydromechanical unit. It goes straight to the sanitary sewer, or to a gravity interceptor with Public Health approval.

Who issues the permit? Public Health Seattle and King County issues the plumbing permit. Seattle Public Utilities issues side sewer permits.

How often does it need cleaning? Before grease and solids fill 25% of it.

Sources

These rules apply in Seattle. Public Health's plumbing guidance also covers Beaux Arts Village, Clyde Hill, and unincorporated King County; other cities in the county set their own plumbing rules.