What exactly do we mean when we refer to a sewage smell that comes and goes in your house? Commonly, the unpleasant odour of rotten eggs is associated with sewage gas. If you are noticing this around your home, it can indicate a variety of plumbing issues. This is especially true if the smell of sewage comes and goes. Read on for tips on identifying and eliminating the cause of sewage odours in your home.

Why Does a Sewage Smell in the House Come and Go?

Due to the frequent movement of water and waste through your plumbing system, and the varying use of different drains throughout the day, some issues can fluctuate. This means that you may only notice the symptoms of a problem, like a sewage smell, at certain times of the day or in response to certain action. For example, the foul smell might be most noticeable when you return home from work and your drains have been unused all day, or during the winter when temperatures are colder. Finding the exact cause of the problem is often a process of elimination and isn’t always easy. Our experienced team of engineers can be there to help identify the issue and provide the right solution to get rid of the foul smell.

Common Causes of Sewage Smells that Come and Go

There are several common causes that can lead to a sewage smell that fluctuates.

Dry P-Traps

A plumbing trap, or P-trap, is the u-shaped pipe you can see under your sinks. Your shower and toilet also feature P-traps, although these may not be visible. The shape of the pipe allows it to retain some of the water, creating a barrier that stops sewer gases and unpleasant smells from moving up the pipe and back into your home. If there is not enough water in the P-trap, gases can escape and cause a sewage smell by the time you return from work.

Blocked Vent Pipes

A vent pipe helps to regulate the air in your plumbing system, which avoids forming a vacuum that can slow or stop the flow of water. It also removes any lingering sewer gases from the system to avoid odours in the home. So if it becomes blocked, the sewage smell can back up and escape into your home. At TWC Draincare, we provide comprehensive drainage solutions that extend beyond ground-level services, addressing drainage issues located at higher levels at your property as well.

Cracked Sewer Pipes

A cracked sewer pipe can release gases directly into your house, leading to the sewage smell. It can also lead to unpleasant visual indicators, like soggy or sunken patches of ground around the property, mould growth, cracks in the foundations of the building, and even the presence of rodents and insects. If you suspect cracked pipes, then don’t delay and call the experts.

Sump Pump Issues

A sump pump is a mechanism that automatically pumps water out of the basement of your home in case of rising water levels, protecting the foundations of your home. An issue with the sump pump can lead to standing water, which often smells like sewage.

Faulty or Old Wax Seals on Toilets

The wax seal around your toilet flange (which connects your toilet to the drainpipe) is designed to create a watertight barrier that prevents leaks of both water and sewer gas. If it is faulty or requires replacing, sewer gases may be able to escape into your washroom, leading to a foul odour.

How to Diagnose the Source of the Sewage Smell

1: Check for Dry P-Traps

• In order to inspect your P-traps, you should place a bucket underneath the pipe and carefully loosen the nuts at the end of the P-trap. You can remove the trap by sliding it downward and gently releasing the contents of the pipe into the bucket.
• Whilst the pipe is open, inspect it carefully for blockages, and then reattach the P-trap and refill it by running the tap for a couple of minutes or flushing the toilet several times.

2: Inspect Vent Pipes for Blockages

• If your drains are gurgling or draining slowly as well as producing the sewage smell, you may have a blocked vent pipe.
• If your vent pipes are the issue, you will need to call a professional. Your vent stacks will usually be located on the roof, and the internal vent system can be hard to get to and difficult to check without specialist equipment. Feel free to contact the TWC Draincare team for advice.

3: Examine Sewer and Drainpipes

• If more than one drain is backed up with water and you are noticing a sewage smell, you may have a more severe blockage or damaged sewer pipe. It’s important to get these drains unblocked, or repaired to prevent the problem getting worse.
• If you have a basement or any crawl spaces on the property, make sure to check them for any water damage or evidence of cracked sewer pipes. These areas are the most common places that issues with your pipes can occur. Since they receive minimal foot traffic within the home, a lot of damage can spread before it is discovered.

4: Test Toilets for Leaking Wax Seals

• If you have an issue with your wax seal, you are likely to notice visible water leaks around the base of your toilet. You can check this by leaving toilet paper where the toilet meets the floor and then inspecting it for moisture absorption.
• You can also check the integrity of the wax seal by conducting a “rock test” on your toilet. Holding each side of the base, gently rock it back and forth to see if it moves. You should not be able to rock the toilet at all, so any motion indicates loose bolts or a breakdown of the wax seal.

5: Inspect the Sump Pump (if applicable)

• If you do have a sump pump on your property, you should inspect it as a potential cause of your intermittent sewage smell.
• Check for water pooling around your sump pump, or any strange noises coming from the pump itself. If you notice any worrying symptoms, give a professional like TWC Draincare a call to come out and service your pump, as this is not something that is typically suitable for DIY attempts.

Fixes for a Sewage Smell in the House That Comes and Goes

Refill Dry P-Traps

• If you suspect that your P-traps are running dry, you should flush your toilets and pour about 2 litres of water down each drain to replenish them. This is a great opportunity to sustainably reuse water after you have had a bath!
• You can also add a couple of drops of mineral oil to each drain to help slow down the evaporation of the water in the P-trap.
• If the issue is not your P-traps, re-filling them will not do any harm.

Clear Blocked Vent Pipes

• Clearing blocked vent pipes can be quite a tricky process. If you suspect that your vent pipes are blocked, call us here at TWC Draincare. Our experienced engineers can utilise the latest draincare technology to inspect and unblock your vent pipes. We will ensure that sewage gases are properly removed from your home, without any unpleasant odours. We pride ourselves on exemplary customer service, which includes no call out charges. Our team will alk you through every step of the work we are conducting and explain how to avoid future problems.

Repair or Replace Cracked Pipes

• If you notice any signs of damaged or cracked pipes, call a professional! At TWC Draincare, we can utilise specialist technology like CCTV drain survey equipment to inspect every inch of your pipes, checking for cracks deep underground to give you peace of mind.
• If any of your pipes require repairing or replacing, our team can talk you through the entire process from costs to timescale, explaining exactly what we will need to do and why.
• If you’re moving home or looking to purchase a new property, make sure a home buyer’s drain survey forms part of your checks alongside your building survey. We’ll use our state-of-the-art CCTV system to inspect the property’s drains and will then provide you with a detailed survey report outlining any issues identified, recommend any corrective action, and give you a copy of the survey CCTV footage.

Replace Toilet Wax Seals

• To replace the wax seal on your toilet, you will need to turn off the water supply to the toilet using the valve behind the bowl, and then flush the toilet to empty it of water.
• Remove the nuts and bolts from the base of the toilet, and then gently rock it back and forth to break the old wax seal. Lift the toilet away from the base to expose the old seal.
• Scrape the old wax seal away with a putty knife, and place the new wax seal in the correct position in the centre of the flange.
• Carefully replace the toilet, ensuring that the seal is secure, using a twisting motion.
• Reattach the toilet to the floor using the bolts and then turn the water supply back on. Flush the toilet and check carefully for leaks to ensure that the seal is secure.

Service or Replace the Sump Pump

A sump pump will require replacement approximately once a decade, as long as it is working correctly and not experiencing wear and tear. The easiest way to ensure that your pump is working effectively is to have it regularly serviced by a professional, who can advise you on any work that may be required to keep it running smoothly.

Frequently Asked Questions

Can weather conditions cause sewage smells to come and go?

Yes, weather can definitely affect the way sewage smells behave in your home. Heavy rain can increase air pressure in your plumbing system, which can push sewer gases back into your living space. This often happens when drainage systems are overwhelmed by excess water. This causes gases to escape through drains, vents, or poorly sealed pipes. In dry weather, P-traps (the U-shaped pipes under sinks and toilets) may dry out if they aren’t used regularly. Without water to block the gases, the smell can leak into your home.

Is a sewage smell dangerous for my health?

Yes, a persistent sewage smell can be harmful to your health, especially if it isn’t dealt with promptly. Sewer gas is typically a mix of methane, ammonia, hydrogen sulphide, and other toxic gases. Breathing in even small amounts can irritate your eyes, nose, and throat. Prolonged exposure can cause headaches, dizziness, or nausea. Hydrogen sulphide, has a strong rotten egg smell and can be dangerous in higher concentrations. This can lead to respiratory problems or even unconsciousness in severe cases. Methane, on the other hand, is odourless but highly flammable. So there is also an explosion risk if it builds up in confined spaces. It’s essential to identify and fix the source of any sewage smell quickly to avoid these health hazards.

How can I tell where the sewer smell is coming from?

Pinpointing the source of a sewage smell can be tricky, but there are a few methods you can use. Start by checking if the smell persists when all windows and doors are closed. This helps confirm whether the odour is coming from inside the house rather than from an outside source. Then, check key areas like sinks, toilets, and shower drains. If the smell is strongest around these locations, it could indicate a problem with P-traps, vent pipes, or a more significant blockage. You can also check for visible signs of leaks or water damage around pipes, which may indicate a crack in the sewer line. If you’re unable to find the source yourself, it’s a good idea to contact a professional plumber who can inspect your system more thoroughly.

Why does my house smell like sewage only at night?

A sewage smell that appears mainly at night can be due to reduced drain usage during the day. When water sits unused in P-traps, it can evaporate, allowing sewer gases to escape into the home. In many cases, this happens in guest bathrooms or other areas that aren’t frequently used. Night-time temperature drops can also cause airflow changes in your plumbing, making odours more noticeable. Additionally, homes tend to be quieter at night, which can make smells seem more prominent when there are fewer distractions. To prevent this, try flushing unused drains and toilets regularly or adding water to rarely used sinks and showers.

Can air fresheners or deodorisers mask the sewage smell?

While air fresheners or deodorisers can temporarily mask the unpleasant smell, they won’t solve the root problem. Covering up the odour may make it less noticeable for a short time, but it can also delay addressing the underlying issue. Ignoring the actual cause can allow the problem to worsen, leading to further damage in your plumbing or the risk of health issues. Sewer gas can indicate more serious problems, like blocked vents, cracked pipes, or dry P-traps, all of which require immediate attention. Rather than using air fresheners, it’s better to locate and fix the source of the odour as soon as possible.

How do I check if my P-trap is dry?

To check if your P-trap is dry, simply pour water down the drain and listen for any gurgling noises. If the smell goes away after doing this, it’s likely that the P-trap was dry. You can also remove the P-trap (the U-shaped pipe under your sink) by unscrewing the nuts at each end and inspecting it for blockages or leaks. If it’s dry, refill it by running the water for a few minutes. For drains that aren’t used often, you can pour a small amount of mineral oil into the trap to slow down water evaporation and prevent the P-trap from drying out again.

What should I do if I find a cracked pipe or leaking vent?

If you find a cracked pipe or notice a leaking vent, it’s important to call a professional right away. Cracked pipes can release hazardous gases and potentially cause water damage to your property, while a leaking vent can result in drainage problems or a vacuum in your plumbing. A professional can conduct a more thorough inspection, often using cameras to check underground pipes or hard-to-reach areas. They can repair or replace damaged sections and prevent further issues, saving you from more costly repairs later on.

Can I fix a faulty toilet wax seal myself?

Yes, you can replace a faulty wax seal yourself if you’re comfortable with basic DIY plumbing tasks. You’ll need to turn off the water supply to the toilet, flush it to empty the tank and bowl, and then unscrew the bolts holding the toilet to the floor. Carefully lift the toilet off the flange and scrape off the old wax seal. Place a new wax ring in position, then lower the toilet back onto the flange, ensuring it’s aligned correctly. Finally, secure the toilet by tightening the bolts and turning the water supply back on. Check for any leaks after flushing to make sure the seal is secure.

What if I can’t find the source of the sewage smell?

If you’ve tried to locate the source of the smell without success, it’s time to call in a professional. Some issues, like blocked vents or cracked pipes, are difficult to identify without specialised equipment. A professional plumber or drainage expert will have the tools to inspect your system thoroughly, including CCTV drain cameras and smoke tests, which can locate hidden problems. Professional inspection ensures that any underlying issue is fixed properly, eliminating the smell and preventing future damage to your home.

When to Call a Professional Draincare Provider

Some drain fixes, like refilling a P-Trap, are easy to complete by yourself. But others, like checking a vent stack or replacing a sewer pipe — definitely require a professional. The time, skill, and specialist equipment that we can provide help keep your home and family safe and secure.

If the sewage smell persists, you may have a complex leak or a hidden blockage. We can identify and fix the problem to give you peace of mind. We’ll make sure that your intermittent sewage smell does not return! We have drain care engineers located all over the UK. This means we can offer rapid responses and we don’t charge for call outs. Whether you’re based in the North East, North Lincolnshire, Greater Manchester or anywhere in between – we can help you. For more information, you can contact our team here.