Recent questions and answers about septic tank size or capacity requirements, set #2. What size septic tank do I need?

This article series provides septic tank size tables to determine the required size or capacity of a septic tank, and it explains how to calculate septic tank volume based on septic tank inside dimensions measured in feet, and we discuss the sizing, installation, and functions of septic tank tees to prevent septic system clogging.

Questions & Answers about Septic Tank Size Calculations & Requirements

These questions & answers about septic tank sizing or size calculations were posted originally

at SEPTIC TANK SIZE - home. You will want to see the tank capacity or sizing tables and guidelines given there.

On 2019-06-23 by (mod) - 2 homes sharing 1 septic tile bed

There are a number of issues with the situation that you described.

Both legal that you need to discuss with your attorney and practical and functional. With a neighbors septic tank draining onto your property you have no control over what's being done or not done properly on that side that isn't going to cause a failure in the system.

We also don't know if the capacity is adequate. It's also unlikely to be a legal installation. I think there could be resale issues as well as septic failure issues.

On 2019-06-22 by Ram

I am in the process of getting a year around cottage. 2 homes shares only Tile bed. This tile bed is in my property. Question is-

1 Having Tile bed in my property is that Safe and OK to have?

2.i have a 3 bedrooms and 1 full washroom so if I plan to put an extra washroom then is the same Tile bed is good enough to handle the job?

3. How often I have to do any maintenance or cleaning for Tile bed. I know there is a pump out for Septic Tank.

Thank you
Ramanan
14166706467

On 2019-05-28 by (mod) -

Have you asked your building department if they have kept records of Prior code requirements?

On 2019-05-23 by Sheila

How would I find out what requirements were in effect in Yavapai County AZ in 1982 regarding septic tank sizing?

On 2018-10-20 by (mod) - septic system size for a 48 bedroom facility

You will need an on-site wastewater treatment system, Thulani. A conventional septic tank and drainfield would have to be larger than you are likely to be able to accomodate.

And you'll need an estimate of the total daily wastewater flow including both the occupants and all other site uses such as kitchens, cleaning &c.

This article series inclues WATER QUANTITY USAGE TABLES that may help you out.

On 2018-10-20 by Thulani M Ndlovu

I would like to build a septic tank to accommodate to 96 people(48) bedroom.I bought a (10000sqm) plot in order to build rented houses.
Kind regards
Thulani
Contact no 0609633554
email mlumax75@gmail.com

On 2018-10-10 by (mod) -

Anon

The weight of a septic tank Varies enormously depending on the materials from which it is constructed. So I'm sorry but I can't give you a single answer.

in addition and getting to the specifics of your question there are no 250 gallon septic tanks. Typically the minimum septic tank size varies depending on local regulations but is likely to be 1200 to 1500 gallons

On 2018-10-09 by Anonymous

How much does 250 gallon concrete septic tank weigh

On 2018-09-26 by (mod) -

10 -50 k$

On 2018-09-26 by Zo

How much is it to have a hole new septic system put in

On 2018-09-02 by (mod) -

You'll need to open the box to see if it's a D-box. Usually a D-box is rectangular as it needs to connect to multiple drainfijeld lines.

If this is a distribution box or other junction box for sewer pipes, I'm unclear why there is what looks like a small hole near the top - to the right of the NSF sticker.

See SEPTIC D-BOX INSPECTION https://inspectapedia.com/septic/Septic_D-Box_Inspection.php

Watch out: if that cover is thin rusted-out sheet metal it may be unsafe.

On 2018-09-02 by Adam

Thanks so much for your comments. The tank diameter is 4.5'(W) X 12' (L) X 5' (D) which would be more than sufficient for my 1 bath use. It is very thick and solid with out cracks or defects.

I agree with your assessment of the white PVC pipe, I can't quite figure what that would be used for. You're correct, more excavation is needed to solve that mystery.

I've attached a picture of the white box with the metal lid. Any idea is that should be the d-box? It is a box that has a National Sanitastion Foundation sticker on the side.

On 2018-09-02 by (mod) - investigate pipes around septic tank

[Click to enlarge any image]

Watch out: for an old septic tank of unknown condition, walking on or near its cover risks falling in and injury or worse, a death.

I do not assume that the septic tank is usable, both by its condition and its size. Further you can't assume that there is a usable absorption field or soakaway.

The molded but un-used side opening is probalbly a knock-out that could have been opened to provide an additional tank inlet or outlet opening.

The small diameter white plastic pipe running alongside the septic tank needs to be understood. You would not run potable water piping right next to a septic tank. The diameter is too small to be a sewer line, though it could have been an amateur drain to the septic tank for graywater, say from a laundry sink. (The diameter looks too small, though).

You need more excavation to understand the dimensions and condition of the tank and further exploration of the site to plan a usable drainfield.

On 2018-09-02 by Adam

I purchased a piece of property that has a septic system on it. I found the tank but I'm not exactly sure what to make of it. First, it does appear to be a cast tank and not a old conder block tank. However, there's no lid on it, it's just a hole that someone put a piece of cinder block over and covered with dirt.

There was an old house (circa 1960) on the property that was demolished before my ownership, so I'm not sure if maybe the contractor who removed the old house broke the lid in the process. When I inspect the inside of the tank, there's a wall to the right with a high opening for either the solids or gray water.

Looking at the tank there's an opening molded in to the side that is not in use and I'm not sure what it is used for. I've attached an image.

Also, it looks like a d-box comes out from it on the side but it's just a plastic box (but does have an NSF.sticker) with a thin metal lid. There's ADS green striped pipe coming out of the side. Have you seen this type of setup before?

On 2018-08-07 by (mod) -

Cecelia

It is perfectly normal and correct for a septic tank to be filled at all times except immediately after having been pumped out for a cleaning.

As waste water enters the septic tank it pushes a like volume of a fluid out of a septic tank and into your soskaway, leach field, or absorption bed.

On 2018-08-07 by Cecilia Ballard

Totally love this info. What a Blessing. I think I have a leak. My septic fills in 3wks max. Pls call 2193312035

How long does it take 3 BR single 1000 gallon septic to fill up that's been capped off. Family of three

On 2018-08-05 by (mod) -

That's what's recommended per that tables above and typical septic codes and standards.

With a smaller tank you can, however, adapt by increasing the septic tank pumping frequency so as to maintain a large net free area and thus improve settlement time in the tank.

In the ARTICLE INDEX see the article SEPTIC TANK PUMPING SCHEDULE

On 2018-08-04 by Cooper

I am about to purchase a 4 bedroom house in NJ. The septic tank on the property is 1,000 gallons. Is that sufficient enough for a 4 bedroom house? Also, how could a house with 4 bedrooms have a 1,000 gallon tank? Shouldn't the house have a minimum of a 1,250 gallon septic tank for a house with that many bedrooms?

On 2018-07-26 by (mod) -

I'm sorry to say, Anna that your question, as posed, is one I can't answer: it's sort of like saying "how much does a house cost?" The range of possible answers, when weh have not one iota of information to narrow down the question, is so huge as to not be helpful. $20K TO $60K or more is possible in generic terms.

You need to know

- the system requirements - daily wastewater flow

- the site size and encumbrances and space available

- the soil properties, percolation rates

- the typical costs for Rhode Island installations

- special encumbrances that affect cost: needing to route sewer pipes under parking area, for example, and cost to safely abandon the existing system.

On 2018-07-26 by Anna V

I'm considering purchasing a 6000 commercial building for retail space.

It has an old septic system that I understand needs to be replaced due to real estate laws in Rhode Island. It was formerly a tool shop. Any idea what this kind of thing will cost me? I have heard horror stories of 20-60K.

I may also want to open a small coffee shop on the site as well. What type of specialist would I deal with to check out and arrange for these types of things? Any info you can provide will definitely help!

On 2018-06-22 by (mod) -

Billy

We're coming from Central Mexico where I'm doing some research.

But to be more clear,

To protect reader trust in our research and articles, InspectApedia.com does not sell any product nor service. We have no business, financial, nor any other relationship with any product or service that we may discuss.

On 2018-06-21 by Billy Fowler

I would like to know where you are coming from, how it will cost me,and what all do you do

On 2018-06-01 by Harry

How big a septic tank needed to handle 38 trailers in a camp site and one other building that uses 3 cubic metre water per day
This building has 7 toilets 6 shower units and 7 hand sinks

On 2018-04-23 by (mod) -

Most likely you'll need a raised bed or mound type septic and probably your septic engineer will propose an onsite mini waste treatment system capable of handling the surge load.

On 2018-04-23 by Jess

We are building on a property thats up on a big rock with just 2 feet of topsoil then hard pan below that that doesn't perk well. Its a home +home office. The main building will have about 3 toilet visits per hour from guests daily for up to 15 hours, and on occasion (every few weeks) events up to 60 people. The standard use will be 4 bedroom house.

What kind of system would be the best for long term. Thank you for your help!

On 2018-03-24 by (mod) - How many days in a row can a septic tank spec'd for a 4 bedroom house handle 15 people?

S

It's not just the septic tank - it's the absorption bed or soakaway bed capacity that's critical.

In the article above see the table titled

Septic Tank in Gallons Size Based on Number of Bedrooms

but a normal 4 bedroom home is assumed to support perhaps 8 people. Your number is double that.

So you probably need a 2000 gallon or 2500 gallon septic tank AND your septic absorption field needs to be able to handle the surge in wastewater volume as well.

See SEPTIC DRAINFIELD SIZE

OR your septic engineer might design a large septic tank with a dosing system to spread out the effluent disposal over a longer period to perhaps permit a smaller drainfield.

See GRAVITY/SIPHON DOSING SYSTEMS
and
see PRESSURE DOSING SYSTEMS

On 2018-03-11 by S

How many days in a row can a septic tank spec'd for a 4 bedroom house handle 15 people?

The house is going to be used as a holiday home so it is only occupied on occasion maybe 30% of the year with variation between 4 to 15 guests during those times. I am looking to purchase it, so it is already built with a "4 bedroom sized" tank (Vermont) just curious if it can handle my families needs from time to time. thanks!

On 2018-02-28 by S Stanley

At what point will water input into a 1,050 gallon capacity septic system likely cause problems?

On 2018-02-28 by (mod) - How much gallons 48×48×72 tank holds

Kg

Let's do the math:

48" x 48" x 72" = 168,888 cubic inches

One U.S. gallon = 231 cubic inches

168,888 cubic inches = 730 gallons

Incidentally that's too small to serve as a septic tank in most jurisdictions.

On 2018-02-28 by Kg Gotti

How much gallons 48×48×72 tank holds

On 2017-10-12 by (mod) -

Sure Anon

48 x 48 x 42" = 103,680 cubic inches of volume in the septic tank, assuming you measured the INSIDE dimensions of the tank (else we'd be off by the wall thickness.

1 U.S. gallon = 231 cubic inches

103,680 cubic inches of tank volume / 231 cubic inches per US Gallon = 448.8 US gallons - nominally a "450 gallon tank" - which is, by the wan, smaller than would be permitted by typical codes in any normal septic system being installed as new work in North America.

On 2017-10-12 by Anonymous

I have a septic tank with these dimisions 48 inches wide × 48 inches long × 42 inches wide How many gallons are there?

On 2017-05-25 by (mod) re: how to calculate the volumes of septic tanks by shape, freeboard, and effects of tank outlet height, sludge & scum layers

Emile,

The volume of a septic tank is calculated based on the shape of the tank - calculating the volume of a rectangular shape

Vol = Length x Width x Height of the rectangular-shaped septic tank.

or for septic tanks that are round or a cylindrical shape and excluding adjustments for ends of a tank that are not flat, you would use

volume of a cylinder V = pi x r² x h 

where pi = 3.1416,

r = cylinder radius (1/2 the diameter) and

h = the cylinder height or length of pipe in our case

Watch out: be sure you use consistent units: feet, inches, meters, centimeters etc. For example if you're calculating the volume in inches and calculate cubic inches of volume you then need to convert to gallons (or liters) where

G = the volume in gallons = 0.004329 gallons per cubic inch

This formula and discussion is

at WELL DYNAMIC HEAD & STATIC HEAD DEFINITION

The actual volume of wastewater in a properly-working rectangular septic tank is easier to calculate than a cylindrical one since we have to consider just the volume of the container up to the bottom of the outlet pipe.

Watch out: you have to remember that a septic tank is never normally full to its top.

If you want to calculate just the "liquid" volume of the septic tank you need to measure the current thickness of the floating scum layer and bottom sludge layer and thus to subtract those from the first volume that you calculated.

The "freeboard" in the septic tank has to be the volume between the bottom of the septic tank outlet pipe (assuming again a properly-working septic system with no blockages in the outlet or drainfield) and the top of the septic tank baffle or tee. That's because any depths higher than the tee top mean that the outlet is blocked and the system is not working normally.

This sketch of a SEPTIC TANK CROSS SECTION shown above and used in several of our articles

inculding SEPTIC TANK LEVELS of SEWAGE illustrates my comments.

Starting at SEPTIC TANK INSPECTION PROCEDURE you can see examples of tools used to measure the scum and sludge layers.

Good luck on your test, Emile.

On 2017-05-25 by emile

how to calculate the volume of a septic tank only for black water? how to calculate the free board

...

Continue reading  at SEPTIC TANK SIZE or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• SEPTIC DRAINFIELD LOCATION for help in finding an existing septic soakaway bed, leach field or drainfield
• SEPTIC DRAINFIELD SIZE
• SEPTIC TANK, HOW TO FIND
• SEPTIC TANKS, CONCRETE
• SEPTIC TANKS, FIBERGLASS / PLASTIC
• SEPTIC TANKS HOME MADE SITE BUILT
• SEPTIC TANK LEVELS of SEWAGE
• SEPTIC TANK PUMPING SCHEDULE
• SEPTIC TANK SIZE
• SEPTIC TANK SIZE vs SEWAGE FLOW
• SEPTIC TANKS, STEEL

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SEPTIC TANK SIZE FAQs-2 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to SEPTIC SYSTEMS

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