A Guide: How To Empty a Porta-Potty

How To Empty a Porta Potty
How To Empty a Porta Potty

When you use the bathroom in your home, you probably don’t give much thought to what happens after you flush. Modern plumbing and sewage systems have allowed us to simply do our business, flush it away, and go on with our lives. 

But what about when plumbing isn’t available?

Portable toilets, or porta-potties, still allow us to do our business and go on with our lives, but unlike our home toilets, porta-potties need to be emptied. This guide will go over how to empty a porta-potty and answer your questions about what happens after your business is done.

How Porta-Potties Work

So, how do porta-potties work when it comes to emptying them? Let’s take a look. Your standard porta-potty rental is a rectangular unit that will come equipped with a few things:1

  • A seat with a lid
  • A urinal
  • A holding tank
  • Toilet paper and a dispenser
  • A lockable door
  • A vent

For the purposes of emptying a porta-potty, we’ll mostly be concerned with the holding or waste tank. Since porta-potties don’t have plumbing and don’t connect to a sewer system, this holding tank is where the human waste and other detritus (such as used toilet paper) is held until the porta-potty is emptied.

You don’t want to keep porta-potty waste sitting around for too long, which is why it is important to have your portable toilet regularly emptied and cleaned. 

Depending on how you’re using your porta-potty, waste disposal and cleaning could happen every few hours or every few days. So, knowing how many porta-potties per person you need for an event or project can help you schedule waste removal and determine the total cost of your portable potty rental.

How Often Do Porta-Potties Get Emptied?

How often do you need to have your porta-potty emptied? It depends. 

The average porta-potty can be used about 200 times before it needs to be emptied.2 At a work site where only a limited number of workers will be using the porta-potty, it may be a while before 200 uses. At an outdoor festival with thousands of attendees, that number may be reached much earlier.

After 200 uses, the holding tank will start to become full. You do not want to get to a point where your holding tank starts overflowing. To avoid this, make sure to have your porta-potties regularly emptied and make sure you have enough porta-potties rented to handle the needs of your event.

What’s In the Holding Tank?

A tank full of human waste sitting around for days isn’t a pleasant thing to think about. Beyond just the potential smell, there’s also a bacterial build-up that can occur. This is why porta-potty holding tanks are filled with the blue liquid you’ve probably seen if you’ve ever used one. This liquid consists of four ingredients:3

  • Water
  • Blue dye
  • Fragrance
  • Biocides

All of these ingredients are important but the biocides serve an especially vital purpose. Biocides are bacteria-killing enzymes that make it safe for human waste to remain in the tank between cleanings. These enzymes also help neutralize some of the odor from that waste.

As for the blue dye and the fragrance, these ensure that porta-potty usage is as pleasant an experience as possible. The blue dye masks the visual appearance of what’s in the holding tank. The added fragrance, with the help of the biocides and the vent, ensures that there is minimal smell in the unit.

Adjusting the Holding Tank for the Weather

The exact chemical makeup of the blue liquid is calibrated to make sure it will hold up throughout the use of your porta-potty. However, when the temperature changes, so too does the makeup of the blue liquid:

  • During warmer weather, the concentration of chemicals needs to be greater. Heat encourages bacterial growth so a higher concentration will be used to neutralize this effect.
  • During cold weather, the concern isn’t bacterial growth—instead, you have to worry about the mixture freezing. For usage in very cold areas, a salty brine may be added to the liquid to lower its freezing point.

Adjusting the Holding Tank for the Times

When porta-potties were first being used, formaldehyde was used instead of bacteria-killing enzymes. While formaldehyde successfully neutralized bacteria, it can be quite harmful, and wastewater treatment plants were not equipped to deal with it. This is why the porta-potty of today opts for enzymes as a safer and greener solution.


How Porta-Potties Are Emptied

Once you’ve got a full (or partially full) holding tank, you’ll need to get it emptied before you can continue using your porta-potty. This is a process that will be undertaken by a professional sanitation worker. In fact, we strongly recommend that you and your sanitation service provider work out a cleaning schedule before you rent your porta-potty. That way, you can make sure it’s properly maintained throughout your usage.

So, what does that professional do for a porta-potty waste removal?3

  • They will arrive in a specialized truck. This truck will be equipped with a vacuum-powered hose, a large holding tank, and a tank of fresh water.
  • The worker will use the hose to vacuum up the contents of the porta-potty holding tank. The other end of the hose will be connected to the holding tank in the truck.
  • Once the worker has removed all the contents of the holding tank, they will clean and sanitize the inside of the porta-potty. As anyone who has ever cleaned a public restroom can tell you, this can be a slow and painstaking job that, at times, can be more difficult than dealing with the holding tank itself.
  • Once the unit is cleaned and sanitized, the worker will add fresh water to the holding tank. They will add the chemical solution of blue dye, fragrance, and biocides to this water.
  • Once finished, the porta-potty will be ready to use again.

At this point, you’ve basically reached the same stage as you do after you flush your toilet. However, the collected waste from the porta-potty still has a final destination it needs to reach.

Where the Waste Goes

When you flush your toilet, the contents start a journey through the sewer system and eventually to a wastewater treatment plant. The contents of a porta-potty’s holding tank will go to the same place—they’ll just hitch a ride on a truck.

Once the sanitation worker has used the vacuum hose to get all the waste into the truck’s storage tank, it will be driven to a wastewater treatment plant. From there, a two-step process begins to properly dispose of the contents.4

Step One: Primary Treatment

The first stage of treating wastewater consists of a process designed to separate and remove solid materials from the water. This is done a few different ways:

  • Screen filter – The first step is to pass the wastewater through a screen filter that will remove any large debris such as twigs or pieces of cloth that has mixed in with the wastewater.
  • Grit chamber – Next, the wastewater is sent into a grit chamber. Here, any sand or stones will sink to the bottom, separating from the wastewater.
  • Sedimentation tank – After the grit chamber, there will still be some solid materials left in the wastewater. They become separated in a sedimentation tank. Once separated, these solids can be treated to make fertilizer, sent to a landfill, or incinerated.

    Step Two: Secondary Treatment

    Once solids have been removed, wastewater still needs to be treated so that organic material and bacteria are eliminated, and you’re left with usable water. This process is accomplished during secondary treatment.

    There are different methods that facilities may use, but one of the most common is the use of chlorine to kill bacteria. In many states, after the chlorine has successfully killed the bacteria, any excess chlorine is removed before the water will be used.

    Overflow Scenario

    Now you know the process for emptying a porta-potty, but there may still be one question nagging at you: what happens if the holding tank overflows?

    Assuming you’ve set up a proper cleaning/emptying schedule, an overflowing holding tank will not be an issue that should occur. However, there is one scenario where the contents of the holding tank may become loose and that’s if the porta-potty unit tips over.

    First things first, this is unlikely to happen. Porta-potties are designed to remain upright, but some scenarios could lead to one overturning:

    • Extreme weather with dangerously high winds.
    • A vehicle or piece of equipment knocking over the unit.
    • A person or large animal intentionally knocking over a unit.
    • A unit being placed on unstable ground and tipping over as a result.

    When you rent your porta-potty, the rental agency will likely inquire about where you’re planning on using it to ensure this last scenario doesn’t happen. However, while rare, the first three scenarios do occasionally occur, and the cleanup is probably as you imagine. It’s still done by a worker and a hose but is now a much messier proposition than when everything is contained in the holding tank.

    Moral of the story: Make every effort possible to keep your porta-potty upright.

    Portable Toilets at ASAP Site Services

    Outdoor concerts, construction sites, home remodels…there are many reasons you may not have access to plumbing and will need to rent a porta-potty. So long as you rent the correct number of units and set up a responsible cleaning schedule, porta-potties are convenient, sanitary solutions.

    If you’re looking to rent a portable toilet, or have any questions regarding other sanitation services such as septic pumping service or shower trailer rentals, ASAP Site Services has all the options you need. Contact us today! We’d be happy to talk to you!



    1. Portable Sanitation Association International. Types of Units. https://www.psai.org/types-of-units  
    2. Portable Sanitation Association International. Special Event Chart. https://assets.noviams.com/novi-file-uploads/psai/PDFs_and_Documents/psai-extended-chart__1_.pdf 
    3. How Stuff Works. How Porta-Potties Work. https://science.howstuffworks.com/innovation/everyday-innovations/porta-potties3.htm 
    4. Environmental Protection Agency. How Wastewater Treatment Works…The Basics. https://www3.epa.gov/npdes/pubs/bastre.pdf 
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