howardsend wrote:

Thank you all for your replies. I had a look at this the weekend and can
report a little more detail. It is large.

There is a second chamber which I couldnt see when I first posted because
the baffle(?) between the two chambers was under the water level ( and it
was dark and I couldnt quite see it!)

The inlet pipe is quite low down the tank side - or whatever it is - and
that was also on the water line at the time I posted.
The following morning when I investigated further it was visable ( water
level having dropped somewhat).

It is a bloody large tank! Much biger than I envisaged but it two chambers
apparently.


Well its an old fashioned but seemingly well made septic tank..

I am not sure what a crust is supposed to look like - will I see it or is it
under the water level? Does it circulate on top somehow? I may in facty have
one I am not sure since I am not sure what I am looking at ( that makes me
sound really thick I am sure but frankly septic tan ks and sewers have
never been high on my agenda previously.

What you get with a septic tank is more or less this.

(i) all suspended solids like sand and grit fall down to the bottom of
the first tank.

(ii) Any light solids go to te top

(iii) most of the organic chemistry takes place in between.

(iv) over time the organics break down into various noxious gases and
various soluble chemicals.

(v) the first chamber is designed to more or less settle out irreducible
solids, and to do the first digestion stage..

(vi) from the first chamber there is a pipe that starts somewhere near
the base of the first chamber - not at the bottom or it get clogged, not
at the top because it picks up nasty floating turdness, but somewhere in
the middle.
This pipe goes into the second chamber, but ends much higher than it
started, the idea being that you want the water level in the first tank
to be high.

(vii)Typically the final outlet from the second (or third) chamber will
be AT the water level of the second or third chamber, as it generally
runs downhill to a stream or soakaway from there.

(ix) Too much silt at the bottom blocks interchamber connectivity, and
needs removing

(x) too much crust on top (looks like peat - actually probably IS peat)
stops final outflow if it extends to the last chamber, and may block
interchamber connectivity if its thick enough..

Thats all about te layers, and why you (occasionally) need to empty
these things.



I have , I think, now cleared the blocked drain and all the crap sailed into
the chamber through the hole followed b y much water that I flushed down to
clear it away.

I have for the moment put the man hole back and am waiting to see how it
goes.

I am unsure whether I need to get it pumped - maybe I should anyway in case
in neds re starting for decomposing since I have been stamping about (
metaphorically) in there.

No. I think if you have no huge crust, and flow is happening between the
chambers, then all is well. However....

My new worry is why my drain blocked. I am not sure b ut I may have a
dropped drain . I rodded down into I thought was about six inches of the
outlet into the tank and hit a block. I rodded back from the tank into the
drain and went back about 18 ins before hitting a block.


Not good. Any trees nearby?

Short of escavating I am not sure how to establish if I have any problem....
or was it just a hard blockage and have shifted it?


Its not that hard to excavate actually. Depending how deep.

A typical problem is that a tree root cracks a pipe, then root hair
fibres get in, and slow the flow down making blockages much more likely.