Can anyone recommend a decent affordable septic tank plus soakaway?

[cowboy25]

This is for a shepherd hut I'm building with the aim of renting out to tourists. Sounds like my local planning authority prefer septic tanks to cesspools which surprised me a little. (I was going to go for an underslung tank attached to the shepherd hut chassis) 

 

Also can anyone explain how the system works? Does all the waste water from showers and sinks get combined with sewage waste and go to the tank? And from there a soakaway means treated waste will soak into the soil? 

 

I'm looking at this tank but it seems some what small septic tank soakaway kits - Septic Tank Kits & Septic Tanks UK | SepticTank.co.uk but I guess if its self emptying that doesn't matter. 

[ToughButterCup]

13 hours ago, cowboy25 said:

...

Sounds like my local planning authority prefer septic tanks to cesspools which surprised me a little

...

 

Legislation does not allow the installation of a septic tank any more. You'll have to have a treatment plant of some sort, sometimes called a digester. 

 

In haste : search for ( here and elsewhere on Tinternet) 'digester' , 'Approved Document H', 'off mains drainage ', and finally 'General Binding Rules' 

 

A local landowner ( of the field next to us) got as far as building a shepherds hut and putting it on his field, but when he did his Due Diligence about renting it, he found the foul drainage issue too costly, and so the hut now sits in his workshop yard.  His point was that renters expect flushing toilets and efficient showers.

 

A Chuck-It-Bucket doesn't cut it  ( his words, not mine -  sorry - its Friday 😑)

 

[JpManning]

ToughButterCup is right that a treatment plant is the usual answer, but it's worth separating Building Regs from the Environment Agency side. Approved Document H puts the options in order of preference: mains sewer, then treatment plant, then septic tank, then cesspool, so building control will usually steer you towards a treatment plant. A new septic tank discharging to a drainage field is still allowed in England under the General Binding Rules, though, provided it's under 2 cubic metres a day, outside a source protection zone 1 and the ground passes a percolation test. What you can't do any more is send septic tank effluent straight into a ditch or stream.

On how it works: yes, everything goes in together, WC, shower and sinks. Solids settle, scum floats, and the partly clarified liquid runs out into perforated pipes laid in gravel trenches, where the soil does the real treatment. None of them are self emptying. Expect a tanker to desludge it roughly once a year, so it needs to be within reach of the hose, about 30 metres.

Two practical points for a holiday let. Do the percolation test first, because heavy clay can rule out a soakaway altogether. And weeks with nobody in can upset a treatment plant's bacteria, so ask suppliers how their unit copes with intermittent use. Check sizing too: Approved Document H sets a minimum of 2,700 litres for a septic tank serving up to four people, and some of the small kits come in under that.

[ToughButterCup]

10 minutes ago, JpManning said:

... Do the percolation test first, because heavy clay can rule out a soakaway altogether. And weeks with nobody in can upset a treatment plant's bacteria, so ask suppliers how their unit copes with [...anything...]

 

Here be dragons.

 

[stevenlee]

JpManning has covered the important bits well. The one thing I would add from the leak side is that the percolation test needs to be an honest one. A drainage field forced into clay will not quietly cope, it will show up as surface water or a soggy garden and that is the kind of job I get called out to later. Also double check your outlet invert level before you buy anything, because without enough fall to the field the whole system struggles from day one.

[cowboy25]

On 16/10/2026 at 12:23, JpManning said:

. Approved Document H puts the options in order of preference: mains sewer, then treatment plant, then septic tank, then cesspool, so building control will usually steer you towards a treatment plant.

 

Yes this is what they have told me, so a septic tank is allowed but not the favoured choice. The mains sewer (if you can call it that) is about 150 metres away and consists of 4 houses whose waste goes into a septic tank and this would involve going under a road so I figure this option is not feasible.

 

So it looks like a sewage treatment plant is what councils want these days over septic tanks? I see they are a little bit pricier. Something like this I assume https://www.owlshall.co.uk/sewage-treatment/sewage-treatment-plants/1-4-bedroom/tricel-novo-6/  

 

can the treated waste from such a sewage treatment plant be then discharged into a ditch or water course? And do sewage treatment plants cope with periods of inactivity better than septic tanks?

[JpManning]

36 minutes ago, cowboy25 said:

 

Yes this is what they have told me, so a septic tank is allowed but not the favoured choice. The mains sewer (if you can call it that) is about 150 metres away and consists of 4 houses whose waste goes into a septic tank and this would involve going under a road so I figure this option is not feasible.

 

So it looks like a sewage treatment plant is what councils want these days over septic tanks? I see they are a little bit pricier. Something like this I assume https://www.owlshall.co.uk/sewage-treatment/sewage-treatment-plants/1-4-bedroom/tricel-novo-6/  

 

can the treated waste from such a sewage treatment plant be then discharged into a ditch or water course? And do sewage treatment plants cope with periods of inactivity better than septic tanks?

Yes, a treatment plant can usually discharge to a ditch or stream, which is the big advantage over a septic tank. In England that comes under the General Binding Rules for small sewage discharges: under 5 cubic metres a day, a plant built to BS EN 12566-3, and the watercourse should normally have flow all year round, so a ditch that's dry all summer won't do and you'd be back to a drainage field. Septic tanks can no longer discharge straight to a watercourse at all. Wales and Scotland run their own rules through NRW and SEPA, so check if that applies. Building control will still want it shown on the plans.

On periods of no use, a septic tank is the more forgiving of the two because it's passive. A plant relies on a live bacterial population and a blower, so after a few weeks empty the biology dies back and it takes a little while to settle once you're back. It's still fine for normal holidays: keep the power on, don't switch the blower off, and go easy on bleach and big loads of washing the first day back. If it'll sit empty for months at a time, mention that to the supplier, as some designs cope better than others.

[Redoctober]

47 minutes ago, cowboy25 said:

So it looks like a sewage treatment plant is what councils want these days over septic tanks? I see they are a little bit pricier. Something like this I assume https://www.owlshall.co.uk/sewage-treatment/sewage-treatment-plants/1-4-bedroom/tricel-novo-6/  

 

 

 

Perhaps have a look at these - https://webuildit-ltd.co.uk/bio-pure-1/ - same ball park figure as above but no moving parts ! Other than a pump you are good to go. We have one and it discharges into a water course the other side of the farmers field, assisted by a connection to the field drainage system.