John Gill Commentary Deuteronomy 15:23

"Only thou shalt not eat the blood thereof; thou shalt pour it out upon the ground as water." — Deuteronomy 15:23 (ASV)

Only you shall not eat the blood thereof
Of the firstling:

you shall pour it upon the ground as water ;
(See Gill on Deuteronomy 12:16), (See Gill on Deuteronomy 12:23), (See Gill on Deuteronomy 12:24).