How Long Does It Take for a Septic Tank to Fill Up?

Whether you have recently installed a new septic tank or are wondering when it is time to run some routine maintenance on your underground septic tank, it is important to understand the workings of the tank and when, if at all, it gets full.

The question of how often you need to pump your septic tank or how long it takes for a septic tank to fill up is one that has been asked for several years now. Some claim that they didn’t know or simply never bothered to pump their tanks, while some suggest that there should be a policy dictating the when and how.

On average, it takes up to 5 years for a regular, on-lot septic tank to fill up. However, this is a very subjective answer. This also depends on how much waste you produce (lifestyle), the tank’s size, amount of solids in the wastewater stream, water usage in the house, and more. Let’s discuss these factors in detail to determine when your septic tank might be full.

Understanding How a Septic Tank Fills Up

A full septic tank

The waste produced in a household is directly proportional to the amount of food consumed in a household. On average, adults discharge about a liter of waste every day, amounting up to 90 gallons per year. Not all of this waste ‘fills up’ a septic tank. In the tank, the waste is reduced to roughly 60%.

Regulatory authorities and the pumping industry both recommend that you shouldn’t let the sludge/scum layer at the bottom of your tank fill more than 30% of the septic tank. Otherwise it could slow down the breakdown process and eventually lead to inefficient processes. After the 305 mark, the process becomes a lot slower, effectively filling up the tank much faster.

It takes about 2 years for this layer to fill up 30% of the tank, after which the hastened pace means that by the 5-year mark, the tank will be filled up to around 98%.

All of these calculations are for ONE person to fill a 1,000-gallon septic tank. For a family that includes a husband, wife, and two children, the same will be reduced to about 1.5 years. As children grow up (school age), this time period will reduce.

Here is a table showing the recommended septic tank size, with respect to the number of rooms.

RoomsMinimum Size
3900 gallons
41,250 gallons
51,400 gallons
61,550 gallons
>62,000 gallons
The minimum recommended size for a septic tank per number of rooms.

So, according to these calculations (as per several state-wide studies), it is safe to deduce that a septic tank should be pumped every two to three years.

Every septic tank has one core function; to retain the sludge that would otherwise be problematic to deal with, while the treated water is distributed to the soil underneath via drain fields. These lighter and floatable solids are what ultimately fill up the tank.

What Happens When the Septic Tank Fills Up?

As mentioned above, many suggest that they never had to pump their septic tank before, yet it seems to be ‘working fine’. Well, this is because as more and more settleable and floatable solids fill the septic tank with solids, some particles begin escaping.

Once the tank is full and there is no more room for the tank to capture/store solids, particles begin seeping through with the water. These are particles that have been settled at the bottom or near the drain pipes long enough to become soft and flow with the water. There are two possibilities from then on:

  1. These particles rearrange themselves to ultimately clog the soil absorption area, thus leading to back flowing toilets and gutters, or
  2. Small solid particles may eventually escape because of the pressure imposed on the bottom layer (because of its weight). This isn’t significant enough to lead to any immediate danger, but with time, as these particles continue to seep into the soil, your property will have a pungent smell to it that both passersby and guests will notice.

This is why it is important to pump your septic tank regularly.

Can I Shower If My Septic Tank Is Full?

You CAN take a shower if your septic tank is full. The only problem you’re likely to face is that of slow drainage. As your septic tank continues to fill up, you will find that the water in the shower, tub, sink(s), and more will start to drain much slower.

Having said that, it is important to note that in some instances, shower drains don’t lead into septic systems but directly into sewage lines, since there is no solid waste within. However, this is relatively rare, considering builders almost always join the shower drains with toilet drains.

Even if the water does lead to our septic tank, since this is just liquid water, you won’t really be doing as much damage to your tank. However, doing so isn’t advisable.  

Will My Toilet Flush If the Septic Tank Is Full?

Your toilet should flush normally up until your septic tank is filled up to 90%. After that, you will find that the toilet starts acting… odd. The toilet will either flush very slowly or the drain will start making odd sounds (such as passing gas or gurgling). It is not uncommon for the toilet to start bubbling.

There is a band-aid solution to this, but keep in mind that this is only temporary. You will need an empty spray bottle, some white vinegar and bicarb soda (baking soda). Alternatively, some acid will do the trick as well.

Simply mix baking soda and vinegar and pour – or pour the acid in. Flush the toilet and it should give you a couple of days to pump your tank without any serious problems.

Signs That It Is Time to Pump a Septic Tank

If you are unable to estimate how long it takes for septic tanks to fill up, you can always go for the ‘cross that bridge when we get there’ policy. For that, you need to know the signs of a filled up septic tank.

One trick (DO NOT TRY THIS) is to simply open the tank and have a peek. Then you’ll likely get sick and spend the next few days in bed – or worse, at the hospital.

On the safer side, you have two options:

  1. Simply get it pumped after a fixed period of time, i.e., 2 to 3 years.
  2. Or you could open the inspection port on the first chamber (as shown in the diagram below) once every year and insert a pole inside. Try to find a pole (or stick) long enough that it reaches the bottom of the tank. These poles may or may not be provided with the purchase. When withdrawing, keep your face away and pull out to see how deep the sludge us. If it is more than 70% of the tank’s depth, you need to get it pumped. Wear proper safety equipment when doing so.


Diagram of a typical septic tank arrangement

We recommend you simply get your tank pumped every 2 to 3 years, unless you know what you are doing.

Septic Tank Pumping Process

A pipe inside a septic tank to empty it
A pipe inside a septic tank to empty it

The best course of action – even for DIYers – is to hire septic tank pumping contractors and let them worry about it. Remember, you don’t just have to pump it; you also have to haul it away to the right facility.

The process begins by breaking the scum layer on top of all the sludge first. However, the sludge itself can’t be pumped out effectively. Professionals then use additives to remove as much sludge as possible. The additives eat away the sludge and reduce its volume. Then, water is added, or it is remixed with the liquid portion of the tank. If there isn’t enough liquid inside, it means you have filled it more than you should have. In that case, you need to add some water from the top.

Mixing is done with the help of a pump, or simply by pumping liquid in, extracting it, and pumping it back in. This ensures all the sludge is mixed thoroughly with the liquid.

The septic system needs to be pumped via the two access ports as show in the diagram above. These are basically manholes (not the smaller one that is used for inspection, above the baffle). Once pumped out, it is common for professionals to check for damage. If any repairs are needed, they are determined at this point.

About Charlie D Paige

Charlie is a massive DIY fan, with dozens of DIY projects under his belt - ranging from tiling to electrics, and concrete pads to walls. Charlie loves tinkering, seeing how things works, the outdoors and playing with power tools... so is it any wonder that he's completed so many DIY jobs over the years?

Charlie loves spreading his hard-won DIY experience with the world via this blog.