Things to do with an old Septic Tank

There is an old concrete Septic tank rearing its head out of the ground in the backyard. The only constructive thing I could think of to utilize it better is make a pond. Other than hiding bodies that is. I popped one of the concrete slabs off the top some time ago to see what could be seen. Lots of mosquito lavae and a roughly 2 metre deep concrete box! Short term I purchased 6 goldfish to put in there to wage war against the mosquito horde that was breeding in there. They did a terribly efficient job of that. and am happy to say about a year later 4 very fat healthy goldfish were removed from the tank! I imagine given some time the gold fish will grow quite large given the huge tank they have.




The water and bottom of the tank were quite clean as the tank has not been used for quite sometime in an effluent nature. Scraping around in the bottom of the tank didn’t stir up anything initially. I’ve been giving the backyard a bit of an overhaul lately and decided that while I was working on some other things out there I may as well be draining the tank. I had previously swapped an old computer motherboard I wasn’t using for a water pump that was also being used in a water cooling setup for a computer. The plan being to use it to pump out the water in the septic one day. The little blighter did a bloody good job considering the amount of lift it had to pump up. It took a bit of fiddling to get all the air out but a bit of Macgyver action involving some poly pipe fittings and garden hoses soon had a reliable way of priming the pump. It basically involved hooking the mains water up to the pump outlet pipe and forcing through a heap of water to clear the air locks then disconnecting the outlet pipe to let the water flow in the right direction.


Being used in a PC meant the pump was 12 volts. I know I have some old ATX power supplies around somewhere but a quick look revealed I had no idea which tub they were stored in. So I just grabbed an old PC I had handy and popped the side off to connect the pump to one of the convenient molex connectors within. Nice small form factor made it a breeze to carry in and out of the shed a couple of time.


You can see it had quite an output at first when the water was closer to the top. This steadily declined as the water level in the tank dropped. It had the tank pumped out with only a few centremetres of water left above the mud that had accumulated in the year or so since I first popped open the tank. You can see below also Kaiser Helping excavate a drainage ditch to stop the water accumulating.


While it was busy being emptied I swondered how the hell I was going to get the fish out with not even a small net handy. Kitchen sieve macgyvered onto an old paint roller handle to the rescue! (Note to self: Buy new Kitchen Sieve before anyone notices it missing) This worked well! Also managed to scoop out some of the mud at the bottom. Mainly old leaves and nectarines that had fallen in from the overhanging nectarine tree.



The tank is all empty now the next steps are to block off the inlet and outlet pipes inside so the tank can fill right up to the brim. It currently fills up from ground water seeping in to about 20cm from the top, it will then slowly seep out to about 40-50cm below the top line after some time with no rain. Hopefully it will rain soon too so I can monitor where the water gets into the tank. I imagine it simply soaks through the cement. It’s possible its coming in through the inlet or something weird though. The house was built in the 1940’s so who knows? I do know the tank remains consistently full all year so there doesn’t seem to be much of a problem with water draining out of it. Once i know it can retain water to the brim I have my eye on some sheets of 100 x 100mm  square high tensile mesh. I’ll cut this to size and dynabolt it into the tank about a foot down from the top of the tank. This is for safety reasons. There’s nothing like a 2 metre pit of doom to keep you on your toes. I could also never let any kids near the back yard unsupervised with a clear conscious. It will however give somewhere to put some water plant pots and still allow the fish to swim through when they turn into giant mutant sized terrors of the deep.

Just waiting on some rain now….

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