Why your dishwasher smells like drains – and the two hidden filters most people forget to clean

Many people notice it on a quiet evening: the dishwasher finishes its cycle, the kitchen is calm, and then a whiff of something unmistakable creeps out when you open the door. It isn’t just “damp dishwasher”. It smells like the sink waste pipe on a bad day.

The good news is that it’s rarely a sign the machine is finished or needs replacing. In most homes, that drain‑like odour comes down to the same simple thing: bits of food trapped in places most owners never touch.

A dishwasher that smells like drains is almost always a dishwasher that hasn’t had its hidden filters properly cleaned.

What’s really causing that drain smell?

Inside every dishwasher, warm water, detergent and food scraps mix and travel through narrow spaces. If tiny particles get stuck and stay wet, they break down. That breakdown releases sulphur‑rich gases – the same family of smells you notice from sink traps or bins left too long.

Modern machines are designed to catch those scraps before they hit the pump or the waste hose. They use a main filter you can see, and one or two “hidden” filters you probably don’t. When those stay clogged, you get:

• Standing dirty water under the filter
• A film of grease coating the base of the tub
• A humid, closed environment that lets bacteria thrive

You smell the result every time you open the door, especially after the machine has been sitting with the door shut.

The filter everyone knows – and the ones they don’t

Most people are aware of the main cylindrical filter in the base of the dishwasher. It twists out, you rinse it under the tap, and you feel virtuous. But the real culprits for deep, drain‑like odours are usually the two less obvious parts around it.

1. The fine mesh plate at the bottom

Under or around the main filter sits a flat, perforated or mesh plate that covers much of the base. Manufacturers design it to trap very small particles and protect the pump. It also happens to be a perfect tray for:

• Grease that has cooled and stuck
• Soft food like rice, pasta and bread mash
• Coffee grounds and tiny vegetable fibres

Because it lies flat, a thin biofilm builds up over time. From above, it may just look slightly grey. From below, it can be coated with a sticky layer that smells powerfully when disturbed.

A lot of owners don’t realise this plate usually lifts out. If you’ve only ever removed the cylinder but never that metal or plastic “floor”, half the grime is still in place.

2. The sump and pump area beneath the filter

Beneath the filter assembly is a small well, often called the sump. This is where water collects before being pumped away. It sometimes includes:

• A coarse secondary filter
• A cover over the impeller (small fan that moves the water)
• Little side channels where debris can lodge

Food that slips past the upper filters drops into this zone. Because it stays moist and is hard to see, it decomposes slowly. The smell that rises from this hidden chamber is exactly the “drain” odour most people blame on their plumbing.

If you’ve never wiped inside that well with a cloth or sponge, chances are it holds a thick ring of residue.

How to deep‑clean those hidden filters safely

You don’t need special tools or chemicals, just a gentle, methodical approach. Allow 20–30 minutes the first time; it’s quicker once you know where everything sits.

Step‑by‑step reset

1. Turn off and empty the machine
   Switch off at the mains if possible. Remove all racks so you can see and reach the base easily.

2. Remove the main filter and base plate

   • Twist and lift out the cylindrical filter.
     
   • Look for clips, tabs or a handle on the flat mesh/plate and lift it out gently. Check the manual if it feels stuck; some slide, others hinge.

3. Soak and scrub the parts

   • Fill the sink with hot water and a squirt of washing‑up liquid.
     
   • Soak the cylinder and plate for 5–10 minutes.
     
   • Use a soft brush or old toothbrush to dislodge greasy film, especially along the edges and underside.

4. Clean the sump and pump area

   • With the filters out, shine a torch into the well.
     
   • Scoop out any visible scraps with kitchen roll (not fingers – there can be sharp bits).
     
   • Wipe around the inside of the well with a cloth dipped in hot, soapy water. Avoid pouring buckets of water in; you just want a thorough wipe.

5. Check the spray arms
   While you’re there, remove the spray arms if they unclip easily. Rinse under the tap and clear blocked holes with a cocktail stick or toothpick so jets don’t drive fresh food back into the filters.

6. Rinse, reassemble and run a hot cycle

   • Rinse all parts under running water.
     
   • Refit the plate and filters carefully, making sure they sit flat and lock into place.
     
   • Run the machine empty on its hottest cycle, ideally with a dishwasher cleaner or a mug of white vinegar on the top rack to dissolve lingering grease.

Most households see a dramatic reduction in odour after a single deep clean of the mesh plate and sump area.

How often should you clean what?

The right rhythm depends on how heavily you use the machine and what you put in it. Think in simple tiers:

Part	How often to clean	Why it matters
Main cylinder filter	Weekly	Stops smells and protects the pump
Flat mesh/plate	Every 4–6 weeks	Prevents hidden grease build‑up
Sump & spray arms	Every 2–3 months	Keeps water flowing and odours down

If you cook a lot of starchy food, roast meat regularly or run the dishwasher daily, lean towards the more frequent end of those ranges.

Everyday habits that quietly prevent bad smells

A few small changes make a big difference. None require pre‑washing everything until it’s spotless, but they do reduce the burden on those hidden filters.

• Scrape, don’t rinse
  Remove large chunks of food into the bin or food waste caddy. Leaving sauces is fine; sending half a plate of curry into the machine is not.

• Avoid heavy grease where you can
  Pour leftover fat from roasting tins into a container, not the sink or dishwasher. Fats harden in pipes and coat filters.

• Load smartly
  Make sure dishes don’t block the spray arms from turning and that nothing covers the filter area. Poor circulation equals more residue.

• Leave the door ajar after cycles
  Letting steam escape reduces humidity inside, slowing bacteria growth and that “stale water” scent.

• Run the hot programme sometimes
  Constant eco cycles at low temperatures are efficient but can allow grease to accumulate. A periodic hot wash helps clear lines and surfaces.

When the smell might be the plumbing, not the machine

Occasionally, the dishwasher is blamed for a problem that starts in the waste pipe. If odours persist despite a thorough internal clean, look beyond the door.

Typical warning signs include:

• The kitchen sink also smells or gurgles
• Water backs up into the sink when the dishwasher drains
• You see leaks or damp patches around the waste connection

In these cases, the issue may be:

• A blocked or partially blocked sink trap
  
• A faulty non‑return valve on the dishwasher waste hose
  
• Poorly fitted pipework that lets sewer gas escape

You can try unscrewing and cleaning the sink’s U‑bend if you’re confident, but a plumber is often the quickest, safest route if you’re unsure.

Simple “reset plan” for the next week

To turn this from a one‑off scrub into a lasting fix, spread a few actions across the coming days:

• Day 1: Deep‑clean the main filter, mesh plate and sump; run a hot empty cycle.
  
• Day 3: Check the filter – it should still be fairly clean. Wipe the door seal with a cloth and warm soapy water.
  
• Day 5: Observe a full wash: listen for odd noises, make sure water drains smoothly, and inspect the base afterward for pooled water.
  
• Day 7: Decide your routine: note on a calendar or in your phone when you’ll next clean the filter and base plate.

Those short check‑ins keep smells from building back up quietly over weeks.

FAQ:

• Do I really need to pre‑rinse dishes? Scraping is usually enough. Heavy pre‑rinsing wastes water and can trick some modern sensors into thinking the load is cleaner than it is, reducing wash power. Just avoid sending large food chunks into the machine.
  
• Can I use bleach to clean a smelly dishwasher? Mild bleach solutions are generally not recommended because they can damage stainless steel and rubber components. Hot water, proper filter cleaning and, if needed, white vinegar or a branded dishwasher cleaner are safer choices.
  
• Why does the smell come back so quickly after I clean? If you only rinse the main cylinder filter and skip the mesh plate and sump, much of the residue stays put. Check you’ve removed and scrubbed all filter parts and that you’re not overloading the machine or running only low‑temperature cycles.
  
• Is it normal to have a bit of water under the filter? A small amount of clean water sitting in the sump is normal and helps keep seals moist. Strong odour, cloudy water or floating debris are not. That’s a sign the area needs cleaning.
  
• My dishwasher is old – is it worth repairing if smells persist? Age alone doesn’t cause odours; dirt does. If a thorough clean and a check of the plumbing don’t resolve the issue, and the machine is also leaving items dirty or leaking, then it may be time to compare repair costs with a modern, more efficient replacement.