lit. don't let one's own fertile water flow into others' field
fig. keep the goodies within the family (proverb)
Definitions (Wiktionary)
proverb
Synonym of 肥水不落外人田 (féishuǐ bù luò wàirén tián, “a benefit should not be given to others and should be shared exclusively among one’s own people”). (syn.) 肥水不落外人田