When a sewer so large that a man can walk inside develops a leak, it takes more than just a simple plug.
Instead, the PUB relies on a technique using strips of PVC that are interlocked in a spiral pattern to form a pipe.
On Thursday, the national water agency conducted a show-and-tell in Kallang on how it has been fixing large sewers with the method called spiral wound lining since 2007.
PUB said this technique is ideal for sewers larger than 60cm in diameter since it can be used even when there is water inside. Other methods require the water in the sewer to be diverted.
Work is usually carried out between 11pm and 4.30am when there is less flow in the sewers. Workers can lay about 20m worth of pipe in a night.
The largest sewer repaired here using this method was in Siglap. Its diameter was more than 2m.
For sewers with diameter smaller than 60cm, a flexible tube is expanded inside and hardened to cover up leaks. This method was used for large sewers before 2007.
The PUB said Singapore has 3,400km of public sewers, of which it has repaired 1,600km since 1996. Each repair is expected to last about 50 years.