Walk into a hardware store anywhere in Pierce or King County and you will find a shelf of septic additives: powders, pods, liquids and monthly subscriptions, sold on a promise to break down solids, revive a drain field or let you skip a pumping.
Washington takes a harder line on those products than almost any other state. The rules are worth understanding before you spend money, because they say something useful that the shelf tag never does.
Two separate prohibitions sit in RCW 70A.105.060, and they are easy to run together.
Since 1 July 1994, no person may use, sell or distribute a chemical additive to an on-site sewage system in Washington. That one is absolute. There is no approved list for chemical additives.
Since 1 January 1996, no person may use, sell or distribute any additive whose ingredients the Department of Health has not approved. Approval runs under Chapter 246-273 WAC, and DOH publishes the list of products that have cleared review. The December 2024 edition runs to more than a hundred products.
Ordinary household products are carved out. Detergent, bleach, drain cleaner and toilet bowl tablets are not additives for the purposes of the statute. What the rule targets is a product sold specifically on a claim that it improves how a septic system performs.
This is the part worth reading twice. In its own publication, the Department of Health is blunt about what it has and has not tested:
Product approval merely indicates that the ingredients are unlikely to cause harm. Denying approval removes harmful products from market availability. The product evaluation does not investigate the validity of performance claims by manufacturers. For this reason, departmental approval and subsequent listing in this document must not be interpreted as certifying effectiveness, endorsing or recommending use of an additive.
Approval is a safety screen, not a performance test. A product can sit on the approved list having never demonstrated that it does anything at all.
There is a second thing worth knowing as a buyer. RCW 70A.105.080 bars manufacturers from using that approval to sell the product, and DOH states plainly that using the word approved in advertising material violates the statute. The Attorney General's office settled on wording manufacturers may use instead: a product may be advertised as complying with Washington laws regarding harm to public health and water quality. If you are being sold a septic additive on the strength of it being state approved, the sales claim itself is improper.
The Legislature took this up in 1993, and the finding it wrote down is unusually direct. It found that most additives do not have a positive effect on the operation of on-site systems, and can contaminate groundwater aquifers, render septic drainfields dysfunctional, and result in costly repairs to homeowners
, and stated its intent to ban the use, sale and distribution of additives in the state unless DOH had specifically approved them.
The regulation exists because the downside was real, not because the upside needed managing.
We maintain the on-site septic service and inspection records filed across Pierce and King County. Across routine and point-of-sale inspections from 2015 to 2025, 18.2% recorded a problem.
Additive use is not a reportable item in those records, so we cannot tell you that additives correlate with anything, and we are not going to pretend otherwise.
What the records do show is which systems run into trouble, and it is not the ones people worry about. In King County, plain gravity systems record a deficiency on about a quarter of routine inspections, against roughly 18% for pressure-distributed systems. The simplest and oldest designs are the ones failing, and age and maintenance history drive that far more than anything you can pour down a drain.
Five things do the work that additives are sold as a substitute for.
There is a legitimate category here, and it is not the retail shelf. Some proprietary and aerobic treatment units specify a particular medium or bacterial charge as part of their manufacturer-approved operation, and some are brought back online after a startup the same way. That is a manufacturer specification attached to a permitted design, installed and documented by a certified professional.
If your system carries that kind of requirement it will be written into your permit record and your operation and maintenance documentation. We check that before recommending anything, and those systems are also the ones the state requires to be inspected annually.
Some are, outright. RCW 70A.105.060 bars the use, sale or distribution of any chemical additive to an on-site sewage system, with no approval route at all. For other additives, it is unlawful to use, sell or distribute one whose ingredients the Department of Health has not approved. DOH publishes the list of approved products, and the December 2024 edition runs to more than a hundred.
Source: RCW 70A.105.060
No. The Department of Health states that approval indicates only that the ingredients are unlikely to cause harm, and that its evaluation does not investigate the validity of performance claims by manufacturers. Approval is not a test of whether the product does anything.
Source: DOH 337-025, List of Approved On-site Sewage System Additives
Because the statute does not let them say approved. RCW 70A.105.080 bars manufacturers from using departmental approval to market a product, and the wording the Attorney General's office accepted instead is that a product complies with Washington laws regarding harm to public health and water quality.
Source: RCW 70A.105.080
No. Pumping physically removes the accumulated solids and scum from the tank. Nothing added to the tank takes them out of it, and manufacturers of approved products are specifically barred from claiming their product eliminates the need for pumping.
No. The 1993 legislative finding behind the statute says in terms that additives can render drain fields dysfunctional. A field that has stopped accepting water is a construction problem and needs a permitted repair or replacement.
A working septic tank already holds the bacteria it needs, and household wastewater reseeds it continuously. There is nothing to boost.
It can be. Some proprietary units specify a medium or a bacterial charge as part of their approved operation, carried out by a certified professional and recorded in your operation and maintenance documentation. Those systems also require an inspection every year rather than every three.
The useful question is what problem the product is meant to solve. Most of the time the honest answer is a pump-out, an inspection or a repair, and we will tell you which one it is.
A Gig Harbor service where the tank itself was sound but the pump tank was not. About 1,400 gallons pumped and the filter cleaned, a gap with roots where the mainline enters the tank, and floats wired so that the pump ran but the high-level alarm stayed silent.
Most residential septic pumping appointments take roughly 30 minutes to two hours, but the actual time depends on the tank size, how easy the tank is to reach, its condition, and how much has built up inside it.
Many Charmin products break down with water and suit a well-maintained septic system, but the product, the amount used and the condition of your tank all matter. What to look for, why flushable wipes are a different question, and when the paper is not the real problem.
King County Public Health inspected food businesses 71,580 times between January 2024 and September 2026, and closed 27 of them. For restaurant plumbing the real risk is not the citation - it is the backup that stops service, and the closure that follows.
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