It's useless saving at the spigot and spending at the bung-hole.

Understand the thought

Meaning in plain English

Saving at one small point is ineffective if resources are escaping much faster elsewhere. Look for the larger source of waste instead of relying on a visible but minor economy.

What the words are saying

The spigot and bung-hole provide an image of two openings with different effects on what a container retains. Restricting a small outlet accomplishes little while the larger escape remains unchecked. The proverb extends this to habits of saving and spending: a person or group may carefully limit one minor use while ignoring a much larger loss. Its useful emphasis is on the whole flow, not on dismissing small economies. A small saving may still help once the larger issue is addressed. The question is whether attention has been directed where it can make a meaningful difference.

Everyday example

A workshop saves scraps of wrapping paper while repeatedly discarding badly measured boards, then decides to correct the measuring process as well.

When to use it

Use it when attention to a small saving is obscuring a much larger preventable waste.

Agent-assisted editorial interpretation. This explains the words; it does not by itself verify their author or earliest origin.