KanjiJLPT N2
Dilute

dilute, thin, weak (tea), pampas grass

Mnemonic

A grass field gets hammered by a violent storm, flooding the soil with rain. The local brewer's specialty herb blend—grown in that grass—is washed out by the storm water, leaving the potion hopelessly diluted, barely more than tinted rainwater.
Additional thoughts
Picture lush grass drowning under a storm, specialty herbs dissolving into nothing—flavor and color fading to almost zero. The three elements combine to drain all potency away.
Quick recall
A grass-grown specialty brew is washed out by a storm, leaving it totally diluted.

Details

The keyword for 薄 is dilute. This kanji conveys the idea of something being thin, weak, or lacking in concentration or density. It can describe physically thin objects, faintly colored things, or liquids that have been watered down and weakened in strength. By extension, it also carries connotations of shallowness, faintness, or something that is light and insubstantial.
On'yomi
はく
Kun'yomi
うす.い、うす-、-うす、うす.める、うす.まる、うす.らぐ、うす.ら-、うす.れる、すすき