How much poo does a septic tank need? + Always do more than one percolation test!!!

[Oxbow16]

Hi all

 

Following on from this thread....

 

 

...things have changed and new questions have arisen, so I thought it best to start a new one.  

 

Firstly, I can't quite remember what inspired it, but we decided to do another percolation test in a different area of the garden and the results were fantastic.  Pretty much perfect for a drainage field.  So we're going to do a third test later next week after there's been some rain.  But things are looking good and if they continue to do so then we're sticking with the septic tank.  Lesson learnt RE doing more than one test.  I'm thinking that the first one was done in an area of high compaction and/or where spoil may have been laid when extensions were built (not by us).  

 

Secondly, for the reasons listed in the other thread I'm still keen on installing a compost loo in the house.  We will keep a flushing loo as well for occasional use and guests who can't get their heads round pooing in a bucket.  But guests are rather occasional here.  So I'm wondering - does a septic tank need poo to function and if so how much does it need?  If for arguments sake the tank only ever received discharge from sinks, showers, washing machine and dishwasher - what would happen?  Would the microbes all die/become dormant?  If so, then what?  

 

Not the nicest topic, but appreciate anyone's thoughts nonetheless   

 

Cheers

 

 

[Gav_P]

I think, but don’t know, that the key to a septic tank is the water flow. 

My view is, less poo = less sediment build up. So will probably never need emptying. 
 

I only got our tank emptied after 4 years as I started to doubt myself... all tank emptying company’s tell you you have to do it every year. But I have read that if it’s working properly, you shouldn’t need to empty it as everything breaks down and eventually makes its way out into the drainage field. .... Turns out mine didn’t need emptying. 

[Gav_P]

Oh and to be fair, emptying only cost £140 anyway. 

[Cpd]

33 minutes ago, Gav_P said:

My view is, less poo = less sediment build up. So will probably never need emptying. 

I have  a BIG septic tank that was  installed a long time ago and I have  no intention of emptying it any time soon...... I have lived on another property  where the septic tank had never been emptied and again it seems to be all about size Of tank and volume of waste going into it.... big tank, small volume of waste = empty once in a blue moon. 

[Onoff]

I only found out "cess pit" after nearly 20 years here. Had it emptied. The fella said to leave some in the bottom so as not to get rid of all the "good" bugs. 

 

 

[PeterW]

Not sure you can install a septic tank these days, has to be a packaged treatment plant. The issue with “flow” is one of capacity as the new ones are multi chamber and that is why they need pumping out - the primary settlement chamber cannot overflow into the secondary chambers otherwise they stop working efficiently. 
 

The bigger issue with treatment plants that they don’t tell you is lack of flow. If they don’t have a continuous flow, nitrate levels can build up in the final stages if the flow is too low - some recirculate the water from the outflow tank to stop this happening back to the start of the process (Biodisc have this as an option). This is needed if the house is not permanently occupied or has varying usage. 

[Russell griffiths]

Not sure I would go to the cost of installing both, if you need a treatment plant then why the compost toilet, if you install the treatment plant it is reasonable cheap to run the pipework from the other toilet to it, you will need pipework for the sinks and showers etc so another 2m of pipe for the toilet will be pennies to put in. 

[joe90]

11 hours ago, Oxbow16 said:

I'm still keen on installing a compost loo in the house.

is that so you can put “it” on your rhubarb? ?

[Oxbow16]

1 hour ago, joe90 said:

is that so you can put “it” on your rhubarb? ?

 

It's part of the reason, yes.  And whilst I might not put it on crops where it is in direct contact with the edible parts of the plant, I definitely aim to use it on fruit trees, berries, etc.  Note however that Joseph Jenkins (Humanure author) uses it on ALL his food crops.  Well rotted for 2 years+ of course.  

 

2 hours ago, Russell griffiths said:

Not sure I would go to the cost of installing both, if you need a treatment plant then why the compost toilet, if you install the treatment plant it is reasonable cheap to run the pipework from the other toilet to it, you will need pipework for the sinks and showers etc so another 2m of pipe for the toilet will be pennies to put in. 

 

It's not a new build.  It's a part renovation on a house.  There's a septic tank here already, and all necessary plumbing/drainage is in place.    

 

2 hours ago, PeterW said:

Not sure you can install a septic tank these days, has to be a packaged treatment plant. The issue with “flow” is one of capacity as the new ones are multi chamber and that is why they need pumping out - the primary settlement chamber cannot overflow into the secondary chambers otherwise they stop working efficiently. 
 

The bigger issue with treatment plants that they don’t tell you is lack of flow. If they don’t have a continuous flow, nitrate levels can build up in the final stages if the flow is too low - some recirculate the water from the outflow tank to stop this happening back to the start of the process (Biodisc have this as an option). This is needed if the house is not permanently occupied or has varying usage. 

 

Septic tanks are perfectly acceptable.  In fact, SEPA and NRW prefer a septic tank and drainage field over a sewage treatment plant and discharge to watercourse.  Not sure what is preferred by EA in England.  I think part of the problem is these people who in the past have said things along the lines of "the discharge from a STP is so clean you could drink it; although I wouldn't personally hahaha".  Well, it isn't that clean, which is why in sensitive areas tertiary treatment is required.  Not only that, but when when the system fails?  Or the pump stops working unbeknown to the occupier?  Or you are away for periods of time and the biological activity stops?  Or you have it installed/emptied and it takes xx weeks for the microbes to repopulate?  Etc etc.  So you raise some good points imo.  I'd stab a guess at the fact that the above scenarios are all likely and common, especially with folks who don't like to get too involved with things like this.  In fact, I was speaking to someone the other day who said he went to do a job and asked the customer why his STP wasn't making any noise?  The customer said it never made noise.  Turns out the air blower hadn't been working at all for 2 years+.  I imagine ignorance is bliss for a lot of people when it comes to sewerage.     

 

What you can't do now is have a septic tank (new or existing) discharging to a watercourse.  

 

 

Thanks to everyone for the responses.  When we were looking for a house to buy we certainly came across many where the septic tanks had not been emptied for an age.  Some were 30 years+.  Some were NEVER emptied.  Personally, and for my low usage, I think I'll go for once every five years or so.  One of the reasons for this is to inspect for damage to the inside of the tank and/or internal pipe work.  On top of that, depending on ow low the pipes are on the T and H pieces, they could be in the sludge area rather than the effluent area if left for a lot of years, which in the end will lessen the life of the drainage field.  Probably what I've learnt most from all this is the importance of protecting the drainage field.  The tank will kind of look after itself if you're sensible with it.  

 

Cheers