More about septic tanks and leach drains than you ever wanted to know

23 02 2021

I live in a semi-rural area. Sewerage lines are not available here and likely never will be in my lifetime. This means that we have to have a septic tank and leach drains to dispose of solid and liquid waste water from the house. We are very careful not to put anything down the waste pipes that could clog them, or could cause ‘fatbergs’ in the septic tank. When such a system is working well, the septic needs pumping out about once every 5 years or so. We moved into this house in 2010, and, as far as I know, the previous owners (who built the house some 3 to 5 years before) had never had the septic pumped. We had it pumped for the first time in June 2017 and some 4500 litres of waste material was extracted and carted away. That’s at least 7 years’ worth of waste, and likely 10 or more years. The extraction people said that we should get it pumped every 3 to 5 years. Oh, one other thing… There’s a lever inside a pipe near the septic tank that I was told by the previous owners that I have to switch over every 6 months. I didn’t know why, but I’ve been really strict about doing that on the 1st of December and June each year. I’ve since found out that it’s the diverter for the leach drains (there are two leach drains).

Fast forward to 1st December 2020… I open the cap over the pipe that houses the lever only to find that the pipe is almost full of waste water. I’d never seen that before. There’d been very little rain, so it must have come from the septic tank or the leach drains. The septic pumping people came out that day and pumped out 4000 litres of waste. The guy told me the leach drains may have collapsed, but if we got the system pumped every two years, the waste water wouldn’t get high enough in the tank to flow into the leach drains. All good. I watched him do his job, then clean out the enormous tank in the ground (he had the big opening open, so I could see there were no roots etc. in the tank and that the tank was in good condition). I like to know how things work, so I was quite fascinated by the whole process.

Fast forward to Saturday 20 February 2021, not quite three months since we had the tank pumped out. The en suite toilet started making gurgling sounds when it was flushed, and the water level would rise a little before falling below the normal level. The other toilet did the same but only for a few hours. On Monday morning I contacted the plumbers to see if it was something we needed to worry about. He said it was likely a small blockage and he’d send someone out tomorrow to run the drain snake through both toilets.

Tuesday morning (today) arrives and I get an early phone call from the plumber saying he’d be there in 15 minutes. Great! It’s going to be a hot day, so it will be good to get this all sorted nice an early and before my work starts for the day. Ha! Little was I to know… When the plumber arrives, he grabs a shovel from the back of his ute. I ask him what it’s for and he says something about waste pipes on the outside of the house (to be honest, I really didn’t take much notice because everything that happened next blew his answer out of my brain). I describe the situation to the plumber (we’re still outside at this point) and take him to where the septic tank is so that he knows where the inspection opening is to watch the toilet water flush through once he’s cleared the blockage. He opens the inspection opening lid…. and the waste level is at the top of the tank!!! It’s totally full, even though we only had it pumped less than 3 months ago and it should take 3 to 5 years to fill.

He spots the diverter pipe and opens it—gross!!!! Liquid waste comes gushing out. He’s able to screw the cap back on, then cleans himself up and calls his boss to see what the next steps are. I also talk to his boss, and a plan of action is formed. The boss will call the septic pump people to come and drain the tank and the leach drains, but while we’re waiting for that, we need to FIND the leach drains. Did I mention this is a VERY lush garden bed (probably because the plants have been sucking up nutrients and liquid from the leach drains for years…)? The plumber starts cutting back bushes and putting down a probe to see if he can find the drains. I know the position of the drains is marked on the house plans, so make a photocopy of that for him. But they are nowhere to be found. He continues digging around the diverter pipe opening area and eventually finds the two pipes that go to the drains—they are certainly not where the plans indicate! We continue cutting back vegetation—this is a big job so I decided to help him, especially as we need to find the drains and their inspection openings before the septic pump people arrive. Did I mention that even at 8am it’s bloody hot?

Within 30 minutes or so of the phone call back to the plumbing office, the septic tank guys turn up. They pump the septic tank (another 4500 litres!!) and give me more information about the purpose of the leach drains and how pumping just the tank and not the drains as well will give us about two weeks reprieve before the tank would need to be pumped again. Why two weeks? Because if the leach drains aren’t functioning correctly, the waste has nowhere to go and so remains in the tank, filling it very quickly. The tank acts as a filter, but the leach drains are the engine. If the engine fails, the filter can only work for a short period of time afterwards. The bottom line is that the leach drains still need to be pumped out, but also we need to find the cause of them not working. The high probability is that the drains have collapsed or that roots have totally taken over (did I mention this part of the garden is LUSH?), or a combination of both. So why didn’t the leach drains dry out as the previous septic people said they should? Well, perhaps they did, but we had some 50 mm of rain about two weeks ago, and that wouldn’t have helped. If they’d been close to capacity, that rain just would’ve added more moisture to the soil and they couldn’t drain the waste into waterlogged soil.

The septic guys and the plumber had left by about 9:15am. The intention was to get an excavator out to the property in a few hours to dig up the garden to find the leach drains. But then the plumbing company suggested that that may not be necessary. The plumber had sent them photos of the pipe arrangement and the garden bed area, and around noon, the plumbing boss came out to check it out and give me a verbal quote and discuss a plan of action. Because we have plenty of room in that garden bed, he suggested that instead of ripping out the whole garden, they rip enough to find the inspection openings for the drains, pump them out, then cap those drains, which have very likely collapsed and need replacing, then leave them in place. Instead of ripping out the drains (and having to cart away all that material, including possible jack hammering to break them apart if they are concrete) and filling the space with replacement drains, he suggested pumping them out and capping them, then using part of the garden bed that doesn’t have as much vegetation on it and is lower (therefore better gravity feed) for the new leach drains.

I’ve decided to go with that as it seems a very sensible solution and preserves a lot of the garden. Not that I’m precious about my garden or particular plants, but it would be nice not to have to look out on a wasteland for a number of years! Even better, after the plumbing company sent the quote (I’d already said to start making arrangements), they said they’d had a cancellation so could do this work on Thursday!

I’ll update this blog post as required. Also, as a side note, the toilets now flush properly! No drain snake needed—just the septic pumped. The plumber didn’t even set foot inside the house, though his timetable for the day was likely very screwed up with all the time he spent cutting back the garden looking for pipes and leach drains.

Update Thursday 25 February 2021

The plumbers came this morning to clear the vegetation and install the new leach drains. I didn’t have to have the other drains found and pumped because they could be capped and left to dry out on their own over time. New pipework from the septic would be used for the two new drains. With a digger and 3 people, it was all done and cleaned up within 4 hours! In addition to the cost (several thousand dollars), I also had the cost of a 5 cubic metre general waste skip bin ($260 for 6 days), but no extra cost for pumping out the old leach drains. The plants can suck on those for a few more months.


Looking north-west from the house to the back driveway, across the top of the partially exposed septic tank and the garden area the plumber and I cleared on Tuesday

Looking back towards the house. Some vegetation already removed on Tuesday and piled up ready for disposal

Starting to dig the first trench; note the amount of vegetation already in the skip bin

Putting together the modules for the leach drain—all that playing with Lego ended up being useful!

Skip bin before being tamped down and only about 30 mins into the operation

Digging the first trench for the 7.5 m long leach drain

Despite what it looks like, the plumber is fiddling with pipe fittings some distance from the digger. Note the roots in the trench—the plumbers suspect root ingress was the reason for the failure of the old drains

The first leach drain, covered in geotextile fabric, is in place and the trench is ready to be filled

The first trench is now filled (note the white diverter pipework on the far right) and the second trench is being dug

The second drain comprises 12 modules side by side, so isn’t as long but is double the width of the other—interlocking modules allow a leach drain to be reshaped to fit the available space

Ready to start backfilling the second trench

All done and smoothed out. The white cap thing protects the diverter that sends flow to one drain or the other (previously I’d switched this over every 6 months to allow one leach drain to dry out while the other took over)

The plumbing company I use prides itself on cleaning up afterwards, and they certainly did that

Not much space left in the skip bin




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