Understanding Septic - Tank Size

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Ditchmonkey

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I have an old steel 500 gallon septic tank that is in bad shape. I'm going to need a bigger one when I replace it to comply with current codes. My question is, what exactly do you gain with a larger tank? Using the following article as reference:

http://home.howstuffworks.com/home-improvement/plumbing/sewer2.htm

both the wastewater in and wastewater out pipes are on the same level, so a larger tank does not provide a larger reservoir to buffer water usage from the house. Therefore, the drain rate must rely on the characteristics of the drain field and have no relation to the tank size. Is this correct? So if my water usage increases, a larger tank will only provide more settling space and I will need to redo the drain field to accommodate the extra water?

I'd love to hear peoples experiences with, or understanding of, the details of septic systems.

Thanks!
 
There will be no extra water or water flow from a larger tank, you are correct that there is only more room for sediment and thats it.
 
It will give room for more solids before they digest. The solid "stuff" you flush does not liquify instantly. It takes time to digest into liquid.
 
People did fine for many years with 200 - 300 gallon tanks. Most of the old systems bipast the septic tank with stuff like the laundry, kitchen sink and shower. My old system had a greese trap tank right before the leach field that took the soap scum out the gray water from the septic also came into that small grease tank. Other people ran wash water into a dry well. Now they want it all to go thru the septic tank. Another reason the bigger tanks are used is more people are being forced into sand mound systems and they require a pump and the pump has to dose the mound with X amount each cycle. they dont want trickle feed they need lots of flow to keep the injection points open.

The majority of your cost wont be in the size of the tank so a 1000 isnt a big deal.
 
Thanks for the replies!

When I purchased the home last summer, the old 500 gallon tank had not been pumped in over 7 years and was doing fine. It seems that a lot of the hysteria surrounding septic tanks is completely unfounded. Unfortunately, the lid of the tank is rusting through so I'm going to have to replace it in the not-too-distant future. I'm hoping to be able to replace the tank and not the entire system.

Does anyone know how the flow rate for the drain field can be calculated? I'm trying to figure out if I add another bathroom and increase water usage whether the current system will continue to function adequately.
 
They do calculate need by the number of bedrooms, but if you are not adding people, there would be no difference.
I guess you could do a perk test in the field to see of the soil is still moving water and or break into the feild pipe to see how much restriction there is as failure to pump for extended periods could cause a problem with solids.
 
Every state has different guidelines and I would suspect Oregon to be on the tougher end of the spectrum. Chances are you are allowed to have what you have because you are grandfathered in. once you start redesigning the system you will have to follow state and local guidelines and my guess is nothing you have will pass even though you are working perfect.

I forget how many years ago I redid mine in Pa but the new unified code was taking effect in two weeks and I called my township and asked what I needed to repair my septic? They said in terms of paper work nothing but I better get the work done in two weeks or less as after that I would have to comply with what the perk test showed in my location and they knew that was going to be a very high sand mound system at least. I rented a back hoe the next day and had gravel dumped in my side yard and built the mound system I wanted and solved all my problems. Now when you drive down my road half the houses have huge mounds in the front yards that look like hell because they couldn’t get a perk test to pass in the back.

If I was in your place I would figure out how to just replace the lid and not change anything until I had a problem. There is a lot you can do to keep your system healthy and going a long time.
 
Haven't had a septic tank since my childhood home got sewers when I was 10 or 11. I believe you'll find in most area's Frodo's by-pass isn't legal. It is pretty commonly done, but not legal.

Getting the tank pumped out on a regular basis is the best bet for keeping it trouble free. The solids will break down but there will always be sludge that doesn't break down. If the sludge gets too deep you can damage your drainfield.

If it is just your lid I'd do a new lid as others have mentioned. A two foot by two foot precast concrete patio tile might be all you need to cover the hole and allow you to backfill.
 
Leach fields are often only rated to last a certain number of years. If you start messing with your current setup you get it condemned and need everything new. I would just try to replace the damaged lid if possible.
 
Out here we have this neat system where the installing company writes the report and it is filed like it was real. When a home buyer wants it checked before buying a house. The comppany comes in a fails the system and files it so now it gets condemmed. Good make work deal.
 
check your codes, black water grey water systems are legal

they are legal here.

what is not legal, but done all the time..daylight the end of your leach field pipe..

your leach field will NEVER saturate
 
When your field goes, you'll know it. Water will start to come to the surface and you might detect a smell when the wind is blowing right. Nj required me to have an engineer design my septic system. The previous one lasted about 19 years. The engineer said he could design it for the amount of bedrooms we were using, but he also knew the amount of bedrooms the house was listed for. The difference would bite me when we were ready to sell, as the the house couldn't be listed for more bedrooms than the field could handle. All that info is on record with the town.
 
Here is a listing, that could be out of date on the use of gray water by state. I didn't read the whole thing, but several states allow a second tank and leach field for laundry water to separate out black water from gray. But they do require a tank, which is in effect a septic tank to settle out solids from the waste water. From the reading I've done on the subject you run the risk of clogging your leach field with link and clots of detergent (especially if you use powered detergent) if you run it directly into the leach field.

Gray water regulations are all over the place on what is allowed and what isn't.

http://greywater-systems.com/regs.htm
 
If your state allows it or if you are doing it anyway you defiantly want a tank before the leach field for non septic gray water.

What I did was run both my septic outflow and my kitchen and washing machine water into a common tank just before the discharge to my mound leach bed. I got my hands on a scrap locomotive air tank and burned off one end and planted it up and down with a couple holes for in and out lines. My tank is about 2’ across and 6’ deep. Inside that tank both in flows 4” have a elbow pointing down. The outflow has a Tee open at the top and with a 2’ pipe going straight down. None of the outflow is glued together for cleaning if required. The idea being with soap and grease and such some will sink some will float and the outflow is taken from the middle of the tank. The leach field / mound is all gravity feed as I had enough drop. But is slightly higher than the surrounding ground. I have 12” gravel base and 4” drain pipe the type with holes on the bottom only, just covered with gravel. The pipes were made into a 16’ square the gravel 24’ square and the square frame has two cross paths. The idea is if any one path got plugged the water could flow around several other directions. My idea was to keep the pipes as high up as I could and they were covered with straw and then just a thin layer of top soil 4” and grass planted. Water can leach down or evaporate up and its worked well for over 20 years now with no smell.

When I have my tank pumped I also have them pump the grease trap and that is a waxy scum a couple feet on the bottom.

I have always felt keeping all the bleach and soap out of the septic helped it work like it is supposed to. I pump mine every 2 years but could easily go 4 or more.

I have photos of the whole thing and if can find them I will post a few. Like I said I could never build that system today with the new laws here. Maybe in some states you still could.

On a side note we have one guy around here they call the midnight septic man. He shows up with a mini excavator and a 5 yard dump truck of gravel about 7:00 pm digs a hole dumps the load in runs a pipe over to your junction box covers it up and hauls away the dirt and is gone before dark in the summer. People do it because that’s all they can afford and it works for another 10 years or more. If you blink you miss him being there. :)
 
The thing is if you are going to run the grey water to the same leach field as the septic tank why not just run it through the tank. It is the same load on the field both ways. I don't get the point of bypassing the tank. It is always full anyway.
 
JoeD said:
The thing is if you are going to run the grey water to the same leach field as the septic tank why not just run it through the tank. It is the same load on the field both ways. I don't get the point of bypassing the tank. It is always full anyway.
Click to expand...

Joe,
I think the theory is to keep the bleach and detergent out of the tank. The bleach isn't going to kill the beneficial bacteria digesting the waste unless you're running a commercial laundry service. You're putting at most a couple of cups a week into a 500 gallon or larger tank with billions of bacteria happily munching away on the sludge.

So I'm with you, run it all through the tank and get it serviced on a regular basis.
 
my illegal system, was installed 10 years ago, has never been pumped out,

it has 2 toilets draining into the tank, the tub,lav,washer,sink, drain into a leach field.
my tank, with only toilets draining into it, is clean, critters are fat wiggling and happy
IMG_1267.jpg



it is the sludge from shaving,and washing hair, that i want to keep out of the tank
the critters are a secondary concern

to me, replacing 100' of 6'' perf pipe, is cheaper than replacing a full tank
or, paying to pump it out every 3 or 4 years at $500 plus per wack
this is only my opinion, works for me.
 
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