Answers to Gospel Questions 5:12; “It is verily true that the Bible as it has come down to us has very little to say about baptism in the Old Testament. Yet there are passages in the writings of Moses and the old prophets which clearly indicate to the prayerful student that baptism was a principle which was practiced all through the days of old Israel. When the temple of Solomon was built, we read of a “molten sea,” ten cubics from one brim to the other, it stood on the backs of twelve carved oxen. This font, or brazen sea, was not used for baptisms for the dead, for there were no baptisms for the dead until after the resurrection of the Lord. It is a logical venture to say that it was used for baptizing the living for the remission of their sins.”

1 Kings 7:23-26; “And he made a molten sea, ten cubits from the one brim to the other: it was round all about, and his height was five cubits: and a line of thirty cubits did compass it round about.  24 And under the brim of it round about there were knops compassing it, ten in a cubit, compassing the sea round about: the knops were cast in two rows, when it was cast.  25 It stood upon twelve oxen, three looking toward the north, and three looking toward the west, and three looking toward the south, and three looking toward the east: and the sea was set above upon them, and all their hinder parts were inward.  26 And it was an hand breadth thick, and the brim thereof was wrought like the brim of a cup, with flowers of lilies: it contained two thousand baths.”

2 Chronicles 4:6; “He made also ten lavers, and put five on the right hand, and five on the left, to wash in them: such things as they offered for the burnt offering they washed in them; but the sea was for the priests to wash in.”

The molten sea in the temple mentioned in the OT was for the priests to wash themselves after they had made sacrifices to God.  They’re not to be used in NT times to be baptized for dead people.

As a Mormon I was baptized for the dead several hundred times.  I went in the first Saturday of every month from the time I was about 12 until I was 16.  Each time I was there I was baptized for 50-250 dead people.