Selective copy and paste of Barne's notes on Matt 3:6 (bold added):
"The word baptize signifies originally to tinge, to dye, to stain, as those who dye clothes. It here means to cleanse or wash anything by the application of water...Washing, or ablution, was much in use among the Jews, as one of the rites of their religion...It was not customary, however, among them, to baptize those who were converted to the Jewish religion until after the Babylonish captivity. At the time of John, and for some time previous, they had been accustomed to administer a rite of baptism, or washing, to those who became proselytes to their religion; that is, who were converted from being Gentiles...It was a solemn rite of washing, significant of cleansing from their former sins, and purifying them for the peculiar service of Jehovah. John found this custom in use; and as he was calling the Jews to a new dispensation, to a change in their form of religion, he administered this right of baptism, or washing, to signify the cleansing from their sins, and adopting the new dispensation...The Hebrew Word (tabal) which is rendered by the word baptize, occurs in the Old Testament in the following places, viz. : #Le 4:6 14:6,51 Nu 19:18 Ru 2:14 Ex 12:22 De 33:24 Eze 23:15 #Job 9:31 Le 9:9 1Sa 14:27 2Ki 5:14 8:15 Ge 37:31 Jos 3:15. It occurs in no other places; and from a careful examination of these passages, its meaning among the Jews is to be derived. From these passages, it will be seen that its radical meaning is not to sprinkle, or to immerse. It is to dip, commonly for the purpose of sprinkling, or for some other purpose...In none of these cases can it be shown that the meaning of the word is to immerse entirely. But in nearly all the cases, the notion of applying the water to a part only of the person or object, though it was by dipping, is necessarily to be supposed.
The following remarks may be made in view of the investigation of the meaning of this word.
1st. That in baptism it is possible, perhaps probable, that the notion of dipping would be the one that would occur to a Jew.
2nd. It would not occur to him that the word meant of necessity to dip entirely, or completely to immerse.
3rd. The notion of washing would be the one which would most readily occur as connected with a religious rite. See the cases of Naaman, and #Mr 7:4, (Greek.)
4th. It cannot be proved from an examination of the passages in the Old and New Testaments, that the idea of a complete immersion ever was connected with the word, or that it ever in any case occurred. If they went into the water, still it is not proved by that, that the only mode of baptism was by immersion, as it might have been by pouring, though they were in the water.
5th. It is not positively enjoined anywhere in the New Testament that the only mode of baptism shall be by an entire submersion of the body under water. Without such a precept, it cannot be made obligatory on people of all ages, nations, and climes, even if it were probable that in the mild climate of Judea it was the usual mode."
This is entirely new to me! I've never bothered to verify the WTS statements about baptism and full body immersion.
Maybe they don't even have the details right?
Craig