Proper Septic Tank to Home Ratio

Hi All,

What is the proper or most opportune home to septic tank ratio? Or should I be asking what is the proper bedroom to septic tank ratio?

The park i’m looking at has 1500 gallon septic tanks, but it also varies from having anywhere from 2 to 5 homes connected to a 1500 gallon septic tank. I suspect 5 homes is easily too much for one septic tank, but is two good? Is three good?

Also, more precisely, is there a general gallon to bedroom ratio? In other words, if it’s a 1000 gallon tank should i only have 4 bedroom attached to it (250 gallons per bedroom), or can i increase the bedroom count. I guess the core question really is what is the gallon to bedroom ratio i should seek to maintain?

Any help would be appreciate.

Sizing may seem small but if you have great percolation rates it may not be a big deal. Best thing to do is have a septic company come out and stress the system to see how it performs under load. Then you will know for sure.

I like the 1 septic to 1 home setup as you can the track tenant behavior to issues with the septic and can charge that back for issues caused by their misuse.

Check your jurisdiction. However design specs are typically 75 to 100 gallons per day per bedroom. With 2 day tank capacity. So 2 homes (3 bedrooms) 2 day capacity is 1200 gallons. Practically the 2 day rule is for solids to settle if you have a screen on outlet of the tanks 5 homes would most likely be fine.

Thanks @jhutson. Thanks @PhillipMerrill, but i don’t quite understand your answer. Can you please expand on it for a newbie? And what does having a “screen on outlet of the tanks 5 homes would most likely be fine” mean? In my scenario – 1500 gallons tanks – how many homes/bedrooms should i hook up to each tank?

The tanks purpose is to catch solids, grease, and scum. To do this the water velocity through it must be low. If velocity is to high or tank is to full solids will blow out to the drainfield and plug it. Tank sizing is calculated to reducing pumping frequency and to reduce velocity to get the solids drop out.
A mesh screen can be placed on tank outlet to keep solids in the tank.

see
http://www.orenco.com/Product_Catalogs

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I have 5 homes per tank. Works fine.
The number of residents on a single tank is directly related to the pumping schedule as opposed to the capacity of the tank. You need to insure the solids on tip do not reach the level of the outlet of the tank. As long as the tank is pumped on a schedule that maintains the solids level above the outlet there is no real limit to the number of residents on a tank.
What you need to do is determine the level of the outlet in the tank and then measure the thickness of the solids floating at the surface to know when to pump. Pump before the solids reach the level of the outlet.
I pump my tanks once per year with each tank having 5-9 residents per tank. Once per year is probably more often than necessary but better safe than sorry when it comes to septic.

I had to built a new septic system for 75 homes two years ago. The engineer’s plan called for a 3,000 gallon tank for each row of 10 homes.

The proper way to maintain a septic system is not to have a pumping schedule, but to have a core sampling schedule and then pumping when it is necessary.

Here is the core sampler I made a few weeks ago for $80. It will reach down 16’ to the bottom of the tanks.

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@Randy_CA Thanks for the info!

@Greg. I appreciate the insight Greg.

There are some wrong answers on here. The correct answer is “whatever the septic system is designed for”. You can have one septic system designed for the entire park, unless it’s really huge. I looked at a park that had 65 homes, all on one septic system. The septic system was only 5 years old, so it was recently designed, permitted and installed.

I took a septic design class in MO years ago, used to have a book on it. There are dozens and dozens of approved system designs.

As far as pumping goes, really Randy has the most correct answer. Residential systems it’s generally recommended to have them pumped every 3-5 years, but this is just a generalized recommendation. One little old lady needs pumped less often than a family of 6 with 4 girls flushing sanitary napkins.

Personally, I’d prefer the one system per park. Easier to maintain IMHO.

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I must say that you do not flush sanitary napkins down toilets. They are designed to dispose of in the trash. I doubt they would make it thru the toilet’s angles.