What You Can and Cannot Put Into a Septic System

The good news? With a little know-how of what you can and cannot put into a septic system, it’s easy to avoid these annoying mistakes.

At Septic Solutions LLC, our local experts in Washington State have seen it all. With 15+ years of hands-on experience, we’ll break down exactly what’s safe to flush and what to avoid—so you never have to worry about a single flush again.

Most people think septic problems start with the tank or the pipes. In reality, they usually start with what gets flushed. Inside that buried system is a living community of bacteria working quietly in your favor. When you treat them right, they keep everything moving without issue. When you don’t, the whole process breaks down—literally.

We’ve seen it first-hand. After handling thousands of septic emergencies across Snohomish County and the Greater Seattle Area, we can tell you that 8 out of 10 failures start with what people put down their drains. Here’s what does the most damage:

• Harsh chemicals – Bleach, drain cleaners, and other chemicals wipe out the good bacteria your system depends on. Without them, solids build up fast and the system fails.
• Non-biodegradables – Wipes, feminine products, coffee grounds, even “flushable” items never truly break down. They clog your pipes, overwhelm your drain fields, and cause you pricey backups. 
• Grease and oils – You may think "what hot grease will do? I'll flush it and everything will be fine." But in reality? It cools down and solidifies into a sticky mess. Over time? It narrows pipes, blocks flow, and can even leach into the soil and water around your property.

And when those issues pile up, the fallout isn’t small. We’re talking sewage in your home, a ruined drain field, and repair bills that can top $10,000. On top of that, Washington State has strict disposal rules, and ignoring them can lead to fines.

At Septic Solutions LLC, our EPA-certified technicians see these issues daily. We’ve helped hundreds of local homeowners avoid disasters and point them out exactly what’s safe. Simple habits prevent costly headaches. And what's worse, improper disposal puts you at risk of violating WA state regulations. And guess what? It leads to fines.

For homeowners throughout Septic System Arlington WA, understanding this is key to protecting your property.

So what not to put in a septic tank? Flushing the wrong items leads to clogs, backups, pricey repairs. Ouch! Our team at Septic Solutions LLC has fixed thousands of systems across Snohomish County and Seattle, and here’s exactly what you should never flush:

• Wipes (even "flushable" ones): Despite labels claiming they’re safe, these items don’t break down in septic systems. Our technicians have pulled out hundreds of wipes from clogged pipes, leading to backups that cost homeowners $500+ in emergency repairs. Always throw wipes in the trash—no exceptions. Even "flushable" wipes can cause major issues; they're a top reason for septic emergencies we handle.
• Grease, oils, and fats: When you pour them down your sink, they cool and harden inside your pipes. This results in blockages that prevent proper drainage. Over time it causes sewage to surface in your yard due to buildup that clogs your drain field. We’ve seen this happen repeatedly in King County homes—always let grease cool and scrape it into the trash. A single greasy pan can cause weeks of problems.
• What chemicals harm septic tank? Chemicals like bleach, drain cleaners, and paint: They kill essential bacteria in your septic tank that break down waste. Without them, solids accumulate rapidly, leading to system failure. In fact, just one bottle of bleach can disrupt the system for weeks. Our team recommends using septic-safe cleaners to keep your tank healthy. Avoid all chemical drain cleaners—they’re a common cause of septic issues.
• Feminine products, diapers, and cotton swabs: These items don’t decompose and quickly clog pipes and tanks. We’ve removed countless diapers and pads from septic systems, causing backups that require immediate attention. Always dispose of them in the trash. Even small items like cotton swabs add up over time.
• Medications, coffee grounds, and eggshells: Flushing pills or ground coffee doesn’t break down. In reality, it clogged your septic system. Eggshells accumulate as solids, increasing pumping frequency.

We’ve helped many homeowners avoid these issues by switching to proper disposal methods. Medications can contaminate groundwater, so always use local take-back programs.

When it comes to septic care, simple is always better. The rule of thumb? If you’re not sure it belongs, don’t send it down the drain.

• Toilet flushables: The list is short—human waste and septic-safe toilet paper. That’s it. Want to check if your toilet paper is actually septic-friendly? Try this. Drop a sheet into a jar of water, give it a good shake, and see if it falls apart quickly. If it does, you’re in the clear.
• In the kitchen: Treat your sink like it’s fragile. Food scraps belong in a compost bin, not in the disposal. If you absolutely have to use the disposal, keep it occasional and flush it through with lots of cold water. For cleaning, choose septic safe products—biodegradable and phosphate-free is what you’re looking for. Old-school methods like vinegar and baking soda work just fine and they don't harm your system.
• Laundry and bath: Liquids beat powders for laundry detergents. Why? That's because powders contain fillers that build up in your tank. In the shower, stick with gentle, biodegradable soaps and shampoos.

"So what things are safe to flush?" Keep it really simple. Based on our 15+ years of septic experience, here's the list of items safe to flush in septic system: waste and toilet paper. Everything else belongs in the trash. Everything else? Toss it in the trash, not the tank. Your system—and your wallet—will thank you.

Want your septic system to last? Great, here's the list of pro tips that our team has compiled for you backed up by our 15+ years of expertise.

The first step? Watch your water use. A leaky toilet or back-to-back laundry loads are not like a big deal. At first sight. Be careful. All that extra water ends up in your tank. And it will cause issues later. How to fix this? Fix drips ASAP. Spread your laundry out quickly. Use low-flow faucets and showerheads. These small changes add up.

What you put down the drain matters just as much. Stick to waste and toilet paper. Everything else—wipes, grease, leftover food—belongs in the trash. Think of it this way: if bacteria can’t eat it, your septic system can’t either.

Maintenance is non-negotiable. Get the tank pumped every 3–5 years, depending on your household size. Waiting until there’s a problem usually means paying thousands instead of a few hundred.

And don’t forget the drain field. No parking cars on top of it. No building sheds. Even extra rainwater should be directed elsewhere. Protect that patch of ground, and your system will quietly take care of you for decades.

Here’s the thing. Septic systems don’t usually fail all at once. They grumble first. If you’re paying
attention, you’ll notice.

Drains that start running slow all over the house? That’s not a coincidence. It usually means your tank’s full or a line is clogging. Then there’s the smell. If you’re catching whiffs of sewage near the tank, the yard, or even inside—it’s not just a bad day, it’s waste that isn’t breaking down the way it should.

Walk out to the drain field. Does the ground feel soggy or spongy under your feet? Puddles hanging around where they shouldn’t? If it stinks too, that’s trouble brewing underground.

And the worst one? Sewage backing up into the shower or toilets. If that happens, stop reading articles and call someone immediately.

Point is, your system warns you. Ignore the hints, and you’ll pay for it—literally.

Your septic system is one of those things you don’t think about until it stops working. And when it stops? Trust me, you’ll think about nothing else. A little care now saves you from a whole lot of pain later.

Of course, no system runs forever without a little help. That’s where we come in. Septic Solutions LLC has been working with homeowners in this area for more than 15 years. Book your inspection today and keep your system working the way it should.