• There are no suggestions because the search field is empty.

Domestic Sewage Treatment Plants: the Dos and Don'ts of Everyday Use

By: Andrew Baird on Jun 6, 2023

A domestic sewage treatment plant relies on receiving normal organic waste in order to work properly. This blog covers the items that can and can’t go down your sinks, toilets, and drains to ensure years of trouble-free wastewater processing.

What is a domestic sewage treatment plant?

If you live or work in an area without a public sewage system you'll need some way of dealing with the wastewater your household or business produces. Traditionally, this has been the function of a septic tank, but following tighter regulation of wastewater disposal, more people are choosing to install a domestic package sewage treatment plant (STP) instead.

How does a small STP treat domestic wastewater?

Compared to septic tanks, STPs treat your waste like VIPs. These systems use bacteria and microorganisms to break down waste and leave you with practically clear water that can be discharged into watercourses.

What goes on in a domestic sewage plant?

First, depending on system type the wastewater goes into a settlement tank (or direct into a biological soup) where with the use of either forced air or a rotating disk, the biology starts to work. Finally, after settlement, the purified water gets sent out into the world to feed the flowers, trees, and other plants via a drainage field and local water courses.

How should you care for your small sewage treatment plant?

Not being on the mains sewage network should make you more conscious of what you’re putting down your loos and sinks, anyway.

That said, there are certainly more stringent rules you should follow to ensure the smooth running of your domestic treatment plant and its longevity.

Bear in mind, that mistreating your STP will not necessarily result in immediate system failure.

But, over time, flushing bulky and non-organic items away can lead to silent blockages in the complex network of pipes that can become expensive engineering problems. Likewise, disrupting the intended chemical balance of the system can silently disrupt its ability to do its job - ultimately affecting the quality of the wastewater you discharge back into the environment.

So, here’s some important advice about how you can optimise your system for daily use.

  • If you have a waste disposal unit, limit its use to prevent overloading the treatment plant. Avoid putting raw or uncooked foods into the WDU and dispose of them in a composter instead.

  • Install grease separators or retention systems upstream of the treatment plant to protect it from grease and fats, primarily in properties with catering facilities.

  • Connect the discharge from condensing boilers to a separate soakaway if feasible.

  • Ensure that the treatment plant is not connected to guttering and drainage systems that collect stormwater or surface runoff. Direct surface/stormwater to a separate storm drain.

  • Do not connect swimming pools or hot tubs to the treatment plant, as the chemicals used in these can impair its performance. Use a separate treatment system for disposing of backwash waters from this equipment.

  • Items like weed killers, fungicides, white spirit, paint, thinners and turpentine can all disrupt the chemical balance in the treatment plant potentially causing clogs, groundwater pollution, and other problems.

What are the golden rules for daily care of an STP?

With all this in mind and the right protective procedures and equipment in place, everyday care of your STP can be distilled into a few basic rules. These are the key messages you’ll need to communicate to family, visitors and workers who live in, visit or maintain your property:

The Dos and Don’ts of STP care


  • Only flush the 3 Ps down the toilet - that is pee, poo and paper

  • Try to use cleaning products little and often

  • Try to spread your clothes washing throughout the week

  • Use liquids, not powders in washing machines and dishwashers

  • Use the manufacturers’ recommended doses of household cleaning products in your white goods - relevant to the hardness of your local water
  • Try to stick to the same washing, dishwasher and other cleaning products - the bacteria will work more efficiently with familiar product

  • Ensure the STP is subject to regular inspections and servicing


  • Pour fat, grease or cooking oil down the sink or drains

  • Frequently changing your brands of cleaners and washing powders

  • Use salt-based water softeners
  • Use household bleach and strong chemicals indiscriminately

  • Tipping bottles of medicine or mouth wash etc. down the sink, toilet or drains
  • Using your waste disposal unit like a rubbish bin - try to use it sparingly

  • Pour any garden chemicals, paint or car engine oil down the sink or drain

Want to download this guide and print it out for reference? Here's a link to your downloadable dos and don't of STP care. 

A last word

Although these lists of restrictions may initially seem daunting, the advice is mainly ‘common sense’ and easy to follow. And given the campaigns waged by national water companies around fatbergs and grease management, responsible use of sinks and toilets for waste disposal should be something we all do naturally, anyway.

A domestic STP is typically the most efficient, cost-effective and eco-friendly solution for off-main wastewater management. And if it is maintained and treated properly, a domestic sewage treatment plant will provide you with years of trouble-free service.

New call-to-action

Topics: Wastewater Treatment

Andrew Baird

Written by Andrew Baird

Andrew is WCS Environmental Engineering Technical Director. Andrew has worked for WPL (now a part of WCSEE) since 2006 and has nearly 30 years’ experience in the water and wastewater treatment industry. Andrew has a background in traditional engineering and technical business development and has worked on technical projects for BAE Systems, North West Water & Yorkshire Water to name a few. Andrews’s commercial awareness goes hand in hands with his excellent knowledge in industrial effluent treatment and broad knowledge of Europe’s water and wastewater treatment needs in manufacturing and process industries.

Sign up to receive our latest insights

Related Posts

Off-mains drainage and sewage treatment for animal shelters

One of the obvious challenges of running an animal shelter, including kennels and catteries, is the need to dispose of ...

How to specify a sewage treatment plant in the healthcare ...

Healthcare facilities such as care homes and hospitals produce higher volumes of wastewater and have more complex ...