paint the Forth Bridge
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!
paint the Forth Bridgeused 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.