Septic Tank Riser Construction — Part 2


There are a lot of photographs, and instead of putting them all in a single download, the Septic Tank Riser was split into two parts. This is the second part of the project.

Second roof cover formwork

Above is the formwork for the second section of the septic tank riser cover.

Second roof cover pour

The second pour. The sides of the excavation has been filled with the rubble that was removed at the start of this work.

Clearing the fill

Removing the fill from the garden

Once the walls were up to the cover height, the rubble in the back garden could be returned to its rightful place — back to where it came from.

When starting the big dig, I counted the number of wheelbarrows that were filled. I would set a target and empty say five, take a break, then another five. Around 150 wheelbarrows, I stopped counting, as five became seven, or was it six, etc. And not once did I thank the thoughtless builders who took such a short cut. I did, however, loose weight and did not have to go to gym. It also caused a calf to pop, loosing at least a month of work.

Some time later of the excavated rubble

Slow progress in removing the rubble.

Bin to remove rubble

Not all the rubble could be returned to the pit, so five bins were required for roughly 12 cubic metres.

Completed side walls

From the inside

Two stages of the roof cover. The bottoms of the top hats can be seen in the set concrete. The side supports for the formwork have been removed, and the internal walls plastered.

Last wall formwork

The final wall taking shape. The last part was on top of the tank, as this wall would be lower than the other three due to the slope of the ground. There were also going to be built-in steps, but that changed to a single step, as it was easy to get in and out, and a ladder could be placed into the hole when needed for lid exposure.

Concrete pour into the above formwork

The last wall did not use brick, but formwork and concrete. The source of bricks was a bit more difficult in the wetter months.

Formwork for the steps

Formwork for the exit to the pit. There were going to be steps, hence the angled reinforcing.

Formwork removed for the step

Another view with the formwork removed for the step.

FOrmwork for inspection drain and last part of wall

The inspection pipe needs to be encased and the last part of the wall with some concrete in a form. Still to be levelled.

From the inside

The last bit of formwork for the walls.

Bucket over inspection pipe

The inspection pipe was encased and a plastic bucket placed over the top. This was removed later so that it could be covered with gravel and then grass if it ever needs to be opened. There were too many “what ifs” to try and sort out some cover, so it was buried much like the previous folk did (but only a few inches to dig).

Plastered outside walls to try and prevent water entry

The walls were plastered to use up the cement that was left over. Even when stored above the ground in a shed, the winters are pretty damp in McLaren Vale, and the bags set as a single 20kg rock if left to their own devices. Hopefully this provided a bit of strength and water proofing, as the formwork was not commercial grade, nor was the concrete vibrated with a proper vibrator.

Almost there

Completed cover and filled in sides

The sides of the tank riser have been filled in with the previous rubble and then covered with top soil that was placed to one side from the original lid exposure.

Bin for removing rubble

One of many bins to remove the rubble. Due to the garage or open carport, the bin had to be placed at the top of the driveway, and all rubble taken by wheelbarrow to the bin. Initially, the bin lid can open so it is simple to run the wheelbarrow into the bin and empty it. Later on, the lid must be closed and the rubble emptied from the wheelbarrow with a spade.


As everything was a trial of sorts, the covering would need to be useful for experiences in a later life. Tiling was old hat by now, but for outside, rightfully needs to be slip proof. Do we do a neat job and go to the edges, or just bury the lid? The decision was made to tile as the washline was nearby, and getting clay on the washing during winter wet months is a cause of much anger! The bricks were a little proud from the cover concrete pour, so an angle grinder was used to level them. A respirator was worn as was eye protection. Obviously hearing protection as well. If this ever becomes my day job, then a Festool pro tool with grinder and vacuum pickup would be first on the shopping list.

Grinding bricks smooth
Tiles on cover

Tiles put on with A66 adhesive — a rubber polymer which allows up to 1mm cracks. We had used this in the house and none of the tiles were loose after three years, nor were there any cracks.

Tiles used for cover

The tiles used for the cover. These were incredibly hard and chewed up plenty of masonary bits and diamond drills. On the packaging, prominent Swiss Quality, but alas, they were made in Vietnam using some Swiss quality system. A bit of misleading advertising — so what else is new?

Being non-slip, they are supposedly porous, so care needs to be taken when cleaning up the adhesive and grouting.

Wine to launch the septic tank

Not all wine is created equal, neither are corks. The launching of the septic tank riser was inspired by the launching of a vessel from the dry dock. Here, we wish to bind the clay rubble that was returned to its rightful place, as it would have ruined friendships if the wine was given away as a gift.

Painted frame for opening

A picture of the welded frame used to seal the top cover opening. It was painted with Luxathane (Dulux epoxy paint).


The tiles were grouted with a Dunlop product that was used with the wood fire tiling some time before, and was much better than the grouting used with the main tiling in the house. Once semi dry, it was cleaned off with a wet sponge, and finally wiped off with a 3M Scotch Brite pad.

Tile grouting
Grouting cleaned up

The grouting has been cleaned up. While nobody was looking, the washline sneaked into the background — here at the top right hand side.

Welded Frame

Not sure who would want to visit this enclosure, but it has to be sealed to protect its valuable contents. Drain cover? Closest thing would be a welded frame, but no time to draw up and get quotes, so we quickly (yeah, right) made one up.

Welded frame corner

The corner of the frame on the welding table. Easy to get 90° and the weld cleaned up here.

Corner of frame in clamps

The frame mitred and clamped, ready to tack.

Tacked from the other side

The other side was tacked, and ready to weld across this side.

The frame was made of two rectangular frames, using angle iron. The one edge would stop the frame falling through the cover opening, and the other edge would stop the lid from falling through. We would also want to keep water out.

Welded frame top to bottom

The upper and lower parts of the frame tacked together.

Testing frame for fit

Testing the frame for fit. We would also have to grind the opening a little and finish off the wall and tiling.

Frame about to be glued in

The welded and painted frame ready to be glued into position.

Sealing the lid frame

Sealing the frame and lid

Either liquid nails or a silicon sealer were used to glue the frame to the cover opening. Water would settle under the frame and rust if not sealed properly. We also sealed the outside once this was glued in place. (Clear silicon sealer).

Frame in place. Glue for bolts to keep water out

The painted frame is glued in place and the edges sealed with clear silicon sealer. The two circles above are to keep water out of the Ramset anchor bolts when the cover is fastened down.

Drilling these holes was more difficult than expected. Two diamond hole cutters went up in smoke, and a small 6mm masonary bit did not last long either. An old German 8mm masonary bit managed to clean out the holes, but at least there were pilot holes to help.

Wooden lid

Ideally, the lid would be made out of stainless steel or aluminium — neither of which I could weld. Time was running out, and I had some Australian Oak that was glued up. There was also some South Pacific Jarrah left over from the side gate, so a frame was put together with Festool Dominoes and epoxy.

Jarrah wooden frame for lid inside welded frame

The Jarrah frame is shown here inside the welded frame before it was glued into position on the tiles as shown further up.

Cover with lid, also showing grass

The cover was bolted down (and a bit of silicon sealer applied). The rental agent required all manner of locks and assurances that an idiot or small child would not stumble into the pit, so to solve the hinge and lock issue, it was simply bolted down. Anyone opening this did so deliberately.

Also shown here is the back garden with the lawn after removing the rubble. The tiles were taken to the edge, then pavers placed next to the tiles so that a weed eater or lawn mower would not try and attack the Nitro tiles. The Australian Oak lid was painted with Luxathane (Dulux epoxy), so we will see how it lasts. By the time it needs to be replaced or the “lids exposed”, hopefully we have stainless steel fabrication expertise.

Lessons Learned

There surely must be some after this mammoth unpleasant task. Here they are: over zealous safety legislators must have come from Consumer Law liability. Nobody will give you information in case they are blamed for the acts of others down the line. Many simply do not know the answers, but in a position of power to pass or fail something.

To the builders who did this in the first place, if there is reincarnation, then next time round, you get to dig a pit with more laws passed in the interim (due to previous experiences and herioc deeds of the legal fraternity). By the same argument, if there is reincarnation, then I did something awful to get this task!

To the previous owners, why dig out the pit a couple of times and then refill the hole?

Would I do this again? Definitely not.

Australian oak lid

The Australian Oak temporary lid. It is a hard wood and it will be interesting to see how it stands up to outdoor weather.


For the benefit of folk purchasing a home or investment property, the cost of placing a septic tank is about $20,000 from discussions with people who told me that was cheap. The assumption is that a digger can access the property or that there is not such a deep hole.

This tank was already installed. The cost in materials was roughly $1,000, plus another $1000 to dump the rubble. The time was not added up, but if used to develop an electronic product, then it really brings on the tears.