A typical call from Northcliff goes like this. A 5,000-litre tank was fitted a few winters ago to catch rain off the roof and feed the garden taps. It has never been opened since. One hot afternoon the hose starts smelling like a pond, and the water in the bucket has a green tinge that was not there in spring.
A torch through the lid tells the story. A few centimetres of silt on the floor, a layer of leaves that got past the gutter screen, and a brown-green film on the walls where the sun has been reaching in through a lid that no longer clips shut.
We pump the water down onto the beds rather than into the drain, shovel and vacuum the sludge out through the lid, scrub and pressure-rinse the walls, sanitise with an anti-bacterial steriliser at the label dose, rinse, replace the split mosquito screen on the overflow, and let it fill.
The lesson: tanks do not announce that they need cleaning. JoJo's own guidance is to check the sludge level every two years. Most tanks in Randburg have never been checked at all.