Tracking the slow progress of my many projects

Cleaning a water tank, the long way

, posted: 2-May-2014 21:59

So I thought I would share the story of how I ended up swimming in my water tank with a vacuum cleaner.

My house gets all its water off an old concrete water tank in the back yard and one day last year it ran dry (or at least down to the slurry at the bottom of the tank).
Turns out some builders we had used to paint our roof had cracked the pipe that connected the roof gutters to the tank and all our rainwater had ended up watering the garden.
My partner was not pleased with her brown tea colored shower, and after calling a water tanker to refill us, I got to researching...

Water tank
Not the cleanest of tanks (the outlet for the tank to our taps is on the left of the image)

I didn't particularly want to spend $$$ each year to clean the bottom of my water tank, especially as they tend to empty your free water out first and fill it back up with their expensive water afterwards. So after some uhmming and ahhhing we settled on a vacuum cleaner, not a pool one though, I found a think called a TankVac

Essentially it is a PVC pipe sucking gunk out of the bottom of your tank, but only when the tank is full to the top and setting up a vacuum on the storm water overflow.

I will let you in on the depths of my procrastination

This all happened last Autumn - It arrived, I half assembled it, It sat around the house in pieces... It moved to the garage... I finally removed the existing storm water overflow pipe...
Now its Autumn again and I have got myself prepared for taking a dip in the water tank (possibly with my camera) to fit the last piece, the part at the bottom of the tank. got into the tank with a ladder and fitted the inner pipes

What an uncleaned tank looks like

Looking out to the daylight

All sealed

Then I will just have to connect it back to the storm water... maybe sometime next Autumn

Does anyone else have experience fitting weird contraptions to a water tank, or fishing/swimming around in one?

Comment by Gavin Stephens, on 3-May-2014 02:09

Can't offer any advice as far as a tank vacuum. One thing you're probably aware of though I thought I'd pass on is my uncle installed a floating filter too. Older concrete tanks usually don't have one but he swears by them for better drinking water. It just floats below the top water line and feeds down to the intake usually towards the bottom of the tank to help take in the freshest water away from the sediment at the bottom. Although the tankvac probably helps to mitgate that.

Comment by nickb800, on 3-May-2014 08:50

I've wondered if it would be much different to make your own TankVac with standard plumbing fittings, and not bother with their proprietary 'siphonic inducer', setting it up as a regular tank overflow system with the intakes spread across the tank floor. Surely this would be cheaper, but I'm not sure if it would be significantly less effective

Comment by pctek, on 3-May-2014 08:56

It doesn't have a release hole at bottom? We have a small plastic one, it has a release....we waterblasted ours, letting the scum out the bottom.

Comment by Sidestep, on 3-May-2014 11:08

We have 8 tanks.

5 are concrete, 20K litre “built on site” tanks, 3 are larger poly ones.
6 of them feed a commercial accommodation, 2 are at our residence.

To prevent most tank sludge, we've fitted leaf slides and first flush diverters, but there's always going to be some sediment settling.

We clean the tanks by lowering the water level and “vacuuming”the final 10 -15 cm out.

The vacuum is a modified vacuum cleaner brush head attached to a flexi pipe on a small electric sludge pump (thanks trademe!)
We pressure wash the tank internally with a weak bleach solution, rinse, suck that out, and they're good to go.

Author's note by Dav4122, on 3-May-2014 14:00

@nickb800 All but a part or two are standard plumbing fixings, some of the reducers look like custom parts

pctek Our tank is partially submerged, the only outlets are the water outlet at the bottom going to our taps, or the storm water outlet at the top of the tank. Hopefully the TankVac will mean we don't need to empty our tank or wait till it is low until we can clean it (the downside being we have to wait till a good rain to fill it and start the suction)

Comment by FlameBeard, on 7-May-2014 09:46

I used to clean em for a job when I was fresh out of school. Did it slightly differently to this though.

Comment by SepticSceptic, on 20-May-2014 14:49

The inside of our water tank looks (and feels) like a mangrove swamp :-(

Almost certain there's an amphibious version of Shrek living in there ,...

Yearly doses of Pour n Go keep the bugs away - after a round of Giardia a few years ago, this is a necessity ....

Spose I should get the property manager to sort out the sludge sometime soon ...

Comment by KShips, on 25-Feb-2015 11:27

Did you get it all setup and working? How do you find it? Any chance of posting another photo of tank water "what a cleaned water tank looks like"?

I have a submersible pump which thinking about just dropping to bottom through manhole to pump out sludge but this looks like cool solution for long term set and forget maintenance.

Author's note by Dav4122, on 28-Feb-2015 12:12

Its all setup and working. The only problem I have found is that the tank needs to be full and overflowing to the stormwater until it will suck the bottom of the tank clean.
Not an issue in winter, but in summer my tank is only half full and it wont be until mid autumn that I get a good suck on the tank vac and empty all the gunk.

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David Hansen
New Zealand

I am a high school technology teacher, living in a renovators dream home, with an interest in good food, and homebrew beer