be like painting the Forth Bridge

To be such an involved or time-consuming improvement process that it never truly ends. The phrase refers to Edinburgh's Forth Bridge, which once required constant upkeep. Primarily heard in UK. Remodeling our house was like painting the Forth Bridge—once we saw how nice one room looked, we had to redo another! Because there's more articles to read, researching is usually like painting the Forth Bridge When you have an ancient hose that barely works, any quick task, like watering the plants, is like painting the Forth Bridge.

paint the Forth Bridge

used to indicate that a task can never be completed.

The steel structure of the Forth Railway Bridge in Scotland has required continuous repainting: it is so long that once the painters reach one end, they have to begin again at the other.