Parashas Metzora · Passuk 14:15
Chabad.org — English translation + Rashi
Torah Temima points to Negaim 14:10.
English: “From the log of oil and he shall pour” — if the log is lacking before he has poured, he may refill it; once he has poured, he must bring another [log] from the beginning.
Deficiency of the log
Chazal distinguish between a deficiency discovered before the pouring (which may be corrected) and one discovered afterward (which requires a new log).