需于血.出自穴.
Xue 血: loan for xue 洫, the irrigation ditches between fields; a small water channel. (古代漢語通假字大字典, p. 769)
鄒漢勳 Zou Hanxun (1805 – 1854) also follows this hypothesis, arguing that the fourth line is at the start of the upper trigram Water ☵ (see 古代漢語通假字大字典).
Chu zi 出自: ‘coming from, going out at’:
妻抱子出自房…
The wife with the boy in her arms came forth from her room…
《禮記 – Liji》
羞出自東房…
The viands came forth from the room on the east…
《春秋繁露 – Chun Qiu Fan Lu》
日居月諸、出自東方!
O sun; O moon,
Which come forth from the east!
《詩經 – Book of Poetry》
出自北門…
I go out at the north gate…
《詩經 – Book of Poetry》
Xue 穴: water course, drain, originating with a hole in a hill or mountain. The Erya 爾雅 explains the word guiquan 氿泉, a spring coming out of a hillside, as:
氿泉穴出。穴出，仄出也。
A spring coming out from the side. Xuchu 穴出 means zechu 仄出, ‘coming out from the side’.
《爾雅 – Er Ya》
Waiting at the ditch coming forth from a hole (in the hillside).