Glossary of Symbols, pg 254; “Brazen Sea. In Solomon’s Temple a large molten sea of brass placed on the backs of twelve brazen oxen (1 Kgs. 7:23-26). It was a baptismal font. Similar fonts, though not made of brass, are found in Latter-day Saint temples for the purpose of performing baptisms for the dead.”
Holman Bible Dictionary; “MOLTEN SEA A large cast bronze basin that stood in the courtyard to the southeast of Solomon’s Temple (1 Kings 7:23-26; 2 Chron. 4:2-5). The basin was cast by Hiram of Tyre who was responsible for all the bronze work in the Temple (1 Kings 7:13-14). The bronze for the molten sea was supplied by the spoils from David’s campaigns (1 Chron. 18:8). The basin was over fourteen feet in diameter, over seven feet high, and over forty-three feet in circumference. It was about three inches thick. The estimated weight is about 30 tons, and the estimated volume is about 12,000 gallons (U.S.). The brim was turned outward resembling a lily, and below the brim were two rows of gourds (but compare 1 Kings 7:24; 2 Chron. 4:3). The sea rested on the backs of twelve oxen. The oxen were arranged in groups of three, each group facing toward one of the four compass directions (1 Kings 7:25; 2 Chron. 4:4). The oxen were later removed by Ahaz and replaced with a stone base (2 Kings 16:17; compare Jer. 52:20). After the fall of Jerusalem in 587 B.C., the basin was broken in pieces and taken to Babylon (2 Kings 25:13; Jer. 52:17). The basin was used for the purification of the priests (2 Chron. 4:6). Some have suggested that the molten sea was also symbolic of the great sea present when God began to create the heavens and the earth thus making the sea symbolic of God’s creative activity (Gen. 1:2). Phil Logan”
As we can clearly see with all the biblical references referring to the brazen or molten sea it was not a baptismal font. It was used for the priests to dunk their hands in the water to wash themselves before they went into the Holy of Holies to sacrifice inside the temple.
The font itself stood outside the temple because as Solomon pointed out the bulls even though made from the earth were considered too filthy of a symbol to be inside the temple walls.
Furthermore, the Israelites weren’t being baptized for themselves or anyone else for that matter before the days of John the Baptist. Communicating with dead people in any way shape or form was strictly forbidden by God.