Sewer System Cleaning

Loud Truck with Tank by Your House?

The Sanitary Sewer Utility cleans the sewer mains using a contractor.  The contractor uses a very large truck, called a vactor truck. These trucks are equipped with large vacuum hoses and water jet hoses. When these trucks are cleaning, sometimes the suction from the large vacuum can impact homes near the cleaning operations.

When cleaning the sewers with vacuum hoses, it is not uncommon to hear gurgling or have some air bubbles in toilets or drains. This is caused by the air moment that the vactor truck creates while cleaning the sewer mainline. Operators work to minimize this air pressure differential by adjusting the water pressure, adjusting the rate of the cleaning nozzle, using specialty nozzles, and venting the upstream sanitary structure.

Municipal sewer cleaning and maintenance – Why?

Sewer cleaning and maintenance usually require water jetting and vacuum technologies, though a variety of approaches and tools. Additionally, there are several reasons why a sewer system receives preventative maintenance – the most common being the removal of debris built up in the mainlines to prevent blockages. Just like our drains at home can eventually become clogged if not cleaned, so can the pipes in the municipal sewer system – but these problems are on a much larger scale.

Water jetting is a common sewer cleaning method to break up the debris to include grease, hair, roots, and rocks to prevent blockages. It involves a long hose with a jetting nozzle to spray water at high pressure, breaking up whatever is stuck in the pipe.  Blockages are often made up of oils, fats, hair, and roots. Once the Jetter eliminates the debris, water will run through the pipes to its intended destination, the City of Snoqualmie Water Reclamation Facility.  Breaking up this debris to prevent blockages often demands a combination approach with loud and noisy equipment.  In emergencies, this may need to occur at any hour of the night.  The utilities' primary responsibility is to maintain a sanitary system and keep the sewer in the pipe and not allow it to be discharged to the environment. That means we need to be proactive and schedule routine cleanings, and, in an emergency, we need to use water jetting to break up blockages and vacuum technology to suck up the debris that created the blockage in the first place.

What are those plumbing vents for on your plumbing system?

How inadequate venting causes issues during vactor cleaning:

• Pressure imbalances: A healthy plumbing vent stack allows sewer gases to escape and fresh air to enter the drainage system, which keeps pressure balanced. Vactor cleaning, however, can cause a sudden and drastic air pressure or vacuum effect. If a home's vent is undersized, clogged, or non-existent, the pressure will seek the path of least resistance—which often leads into the house. This can result in a gurgling of water, or the water in the drains or toilet to be sucked out of the bowl, or toilet water "blow out."  
• "Blow out": The sudden pressure differential in the sewer main forces air up the home's service line and if the volume of air doesn’t exit through the building vents it will cause the water in the residential plumbing system to blow out of the drain. This is usually more noticeable on a drain or toilet that is located at the lowest point in the house.
• Siphoning and sewer gas intrusion: A powerful vacuum effect can also occur during vactor cleaning, which may draw the water right out of a home's P-traps. The P-trap's water seal is what prevents sewer gases from entering your home. Once the water is gone, the seal is broken, allowing sewer gases to freely enter the building.  The water in the p-trap should only be able to feel the force of the vacuum if the building's vent system isn’t adequate to handle the volume of air flow.  For this reason, if you experience issues when the city is cleaning in your area, it is a good idea to run water in your drains for a few minutes.  We normally clean in each area every 3 to 5 years.   Any issues you experience will be minor and very infrequent.

What can homeowners do?

• Get a professional inspection if your house's drains are slow, or you hear gurgling when running water down drains in your house: If your home's plumbing vents are inadequate, the problems will persist. Consider a full plumbing inspection to ensure the vent system is properly installed, sized, and clear of blockages like leaves, nests, or other debris.
• Be aware the utilities are required to clean the sewer system: If you are a property manager or concerned resident, understand that the City cleans the sewer pipes as a preventative measure on a 3-to-5-year schedule to minimize sewer blockages from grease and other undesirable items that are flushed down the drawn at homes and businesses.   If you see, hear, or smell the truck in your area, this is a good indication that your sewer system is being cleaned to maintain a properly operating and sanitary system.
• Take precautions if cleaning is scheduled, or you see the truck: You can put towels over toilet bowls or floor drains to help minimize the effects of a pressure imbalance. However, addressing the root cause—inadequate venting—is the best long-term solution, or install a backwater valve.

Issue: Smells Like a Sewer

Sometimes pockets of air from the sanitary sewer can bubble up into your home while the mains are being cleaned. If a sewer gas smell is present in your home:

• Run water in each sink for a minute or two
• Flush all your toilets
• Pour a couple of gallons of water down any floor drains (the water in the traps may have been pulled out from the cleaning of the main)

Issue: Vactor Truck Blew Sewage out of my Toilet/Sink/Floor Drain

While sewer utility operators work to prevent this scenario from happening, there may be some situations that are not avoidable. In severe cases, the homeowner should contact Public Works Operations and discuss the issue at 425-831-4919. Hours of operation: Weekdays: 7 am-3:30 pm.   We will actively work with property owners to help prevent this from happening again in the next cleaning cycle.
 
 Things homeowners can do to prevent this from happening:

• Install a sanitary sewer backwater valve.  The backwater valve is not required under city code currently, but they are recommended by utility operators, and most homeowner insurance policies usually provide a discount if one is installed.  
• Make sure your home is properly vented and have your vent stack inspected for any type of blockages (sticks, nests, leaves).
• Make sure that the toilet seat is down when the vactor trucks are in the area and place a towel on the floor and over the toilet seat to help avoid blow out if you have experienced issues in the past.