Garbage Disposals and Septic Systems in Lake Stevens, WA

Last updated: October 2026

Snohomish County has roughly 84,000 septic systems, and plenty of Lake Stevens homes outside the sewer district run on one. If your kitchen has a garbage disposal — or you are thinking about adding one — here is the honest version of how disposals and septic systems get along.

Why do disposals and septic systems need extra care?

A septic tank works by settling: heavy solids sink and form sludge, lighter material floats as scum, and the clearer liquid in the middle flows out to the drain field. The system is sized for normal household wastewater. A garbage disposal roughly doubles the food-waste solids going in, which means sludge builds up faster and the tank reaches its pumping point sooner.

None of that is a dealbreaker — it is just math. The problems start when the pumping schedule does not change to match. An overfull tank lets solids carry over into the drain field, and a clogged drain field is the expensive failure: field replacement commonly runs into five figures. The disposal is never the direct cause; neglected pumping is. But the disposal makes neglect costlier, faster.

What are the best practices for a disposal on septic?

• Scrape plates into the trash first. The disposal should handle small scraps and rinse-off, not full plates of food.
• Run cold water before, during, and after. Cold water keeps fats solid so the disposal can break them up and flush them through, instead of letting them melt and re-coat the pipes. (Better yet, keep grease out entirely — see our FOG guide.)
• Feed it slowly. Small amounts at a time, with the water running. Stuffing it full is how jams and clogs start.
• Pump the tank more often. With regular disposal use, plan on every 2 to 3 years instead of the usual 3 to 5, and let an inspection set the real interval for your household.
• Skip the "septic-safe" additives. No powder or liquid replaces pumping. Bacteria additives are not a substitute for removing sludge.

What should never go in the disposal?

• Grease and cooking oil. Coats pipes and adds to the scum layer. Trash it.
• Coffee grounds. They do not break down; they settle into sludge.
• Fibrous vegetables — celery, artichokes, corn husks, onion skins. The fibers wrap the impellers and form mats.
• Potato peels, pasta, and rice. Starchy foods swell into a paste that clogs drains.
• Eggshells in quantity. The membrane and gritty shells add up in the tank.
• Bones, pits, and shells. Bad for the disposal on any system, septic or sewer.

When should you skip the disposal entirely?

Be honest about your system. Skip the disposal — a sink strainer and a trash can work fine — if your tank is older or undersized, if you are already pumping more often than every 3 years, if the drain field has a history of trouble, or if the household will not stick to the "small scraps only" rule. A disposal that gets used like a trash can on a marginal septic system is a drain-field replacement waiting to happen.

Also note: some jurisdictions size septic tanks larger when a home has a disposal. Whether that applies to your property depends on local rules. If you are unsure whether you are on septic or sewer at all, our septic vs sewer guide walks through how to tell, and our septic services page covers inspections, pumping coordination, and repairs.