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I've got an old underground rainwater tank with a seriously deep layer of mud and gravel of a weird blancmange/jelly/wet concrete consistency at the bottom. I'd like to clean it out, but my sump pump won't shift it - too gooey - and the septic tank emptying firm's truck hadn't got enough suck - it's 4.5m or so deep. The access is 18x 24 inches. Any suggestions?
Perhaps it needs partly filling with water and stirring so the septic tank co (or your pump) can suck it out? Not sure what to stir it with - perhaps a pressure washer lance on a pole?
Would still have the gravel to deal with - put a filter on the pump input!
Someone should be able to get through a 18" x 24" opening (an ex potholer?) then rope,bucket and spade?. as long as its only been used for rain (no nasty methane gas etc)
Thanks for your thoughts Joe and CW. It looks as though I can hire a heftier pump more suited to dealing with slurry, but I'm still going to have to stir it up quite a bit with the pressure washer, as you suggest. Watched by my anxious spouse I went down inside yesterday and survived to tell the tale - I think the main hazard now is stepping off the ladder and getting stuck in the mud, which grips like hell.
There must be about 500 bucketfuls of gunge to remove, so I'm hoping to avoid the rope and bucket method at least for the bulk of it
I went potholing in Derbyshire once, and didn't like it much - this feels a lot safer.
Don't go in there without a rope around you and someone strong enough to pull you out. You won't necessarily have a "hard to breath" sensation before you pass out.
Caves are inherently fairly safe because they are created by disolving limestone with water over millenia but going down them is not everyones cup of tea (I did a lot of it years ago). If there is that much gunk I dont blame you for hiring a pump for the bulk of it. When you do go down to clear the last bit see if you can borrow a canary from someone!!!! tho I dont supose that would keep H&SE happy.
If and when you get it cleared out (my approach would be plenty of dilution and use the gully sucker) you might want to look at either inlet filters or a small settlement tank that is easy to clean. Stop the stuff getting in is probably the best long term approach.
It was a long haul, but I'm just celebrating the end of my cistern clearing. I ended up using a jetwash lance on a pole, alternating with a 20ft long 'egg whisk' on a slow drill, plus getting down there with a garden fork to break up really solid stuff lower down. Also good was pumping the water up to my trailer, and then syphoning it back down in a directed flow via a long 2" tube. Round and round it went until really good and gloopy, and bringing the gravel up with it. I recon I shifted getting on for 10 m^3 of sediment. Hours of fun.
Thanks for your thoughts and concern for my safety. I heeded your advice.