We have a working septic system that we have no complaints about.

However, we'd like to add a guesthouse and more bedrooms and that requires expanding the septic system.

I am happy to do this and happy to spend whatever it takes to do it.

However, I insist on a simple system relying on gravity and no pumps.

The problem is that our available leach field is relatively small ... we need something like 8400 square feet and we have something like 3500-4500 square feet.

The solution suggested is to pump effluent uphill, elsewhere, where other field space can be found.

My question:

In general, are there practices that can reduce leach field area?

For instance, could we cascade from one septic tank to another and the resulting effluent is ... thinner ? Needs less leach field?

Interested in any and all comments and suggestions - thank you.

  • you could move your house and septic system up the hill (then gravity could work) , but that doesn't seem like an attractive solution.
    – Jasen
    Nov 25, 2019 at 7:39
  • Effluent is effluent cascading from one to another tank will not result in less effluent. The answer from Lee Sam will result in less effluent. Your local AHJ will have to be involved in whatever system you settle on and they will have lots of opinions and rules that will have to be followed to get permits.
    – Kris
    Nov 25, 2019 at 18:02

2 Answers 2


I know you said "However, I insist on a simple system relying on gravity and no pumps", but I am going to ignore this and suggest you consider a mini-sewage treatment works.

We used to own a house with a Klargester biodisc, and it ran without problems for the 10 years we owned the house. The outflow was clean enough to discharge into a ditch. One of the advantages of the Klargester is that there is no leech field to get blocked, and if the pump does need to be worked on, it is reasonably accessible.

We did have a problem with the electrical supply (which I fixed by replacing the wire with an armoured cable). Before I did that, we had to switch off the Klargester when the ground was very wet (otherwise the RCD/GFGI tripped); this means I know that leaving the Klargester without power for a couple of days every so often is not a problem.

  • Wow - thank you - this is very interesting ... my requirement of no pumps is because we are in northern california and even before the public safety shutoffs, 48 hour outages were common each year, and now we just had a 96 hour outage - but this looks like it would be fine ... I was going to ask you if this is a solution available in the united states, but I see that they have a US division ... now to find out if it is code compliant where I live ...
    – user227963
    Nov 25, 2019 at 15:34
  • Also, do I understand the biodisc is the entire solution and no tank is involved ? I am skeptical that this can get permitted by my county agencies, but I will ask ...
    – user227963
    Nov 25, 2019 at 15:38
  • There is a tank divided in two. The bio disk is a series of crinkly disks spot welded together and arranged so that half the disks are in the dirty water, and half in the cleaner water. The biodisk rotates slowly (once or twice a minute) so it builds up an aerobic bacterial film (which does the work). There is a cup attached to the biodisk so that each rotation a cup-full of "dirty" water is poured over the top of the "clean" disks (thus transferring water from the dirty side to the clean side). I would avoid drinking the outflow, but I wouldn't head straight to hospital if I did. Nov 25, 2019 at 15:51

You could separate the “grey water” from both houses and send it in a different direction or to a deep drywell that requires less space.

  • Some locals may not allow this. I wanted to separate my washer rinse water out and the health dept said they would not allow that. I think it's a great idea though and know a lot of folks who have done it anyway.
    – Dano0430
    Jun 6, 2023 at 15:59

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