"Anciently, a fuller was one who cleansed and whitened garments. 'The process of fulling or cleansing clothes consisted in treading or stamping on the garments with the feet or with bats in tubs of water, in which some alkaline substance answering the purpose of soap had been dissolved' (Peloubet, 203-4).
"Christ's blood is the only 'fuller's soap' strong enough to remove all stains of sin from those who repent and fully accept his atoning sacrifice (1 Ne. 12:11; Mosiah 3:11-18; Alma 5:27; 13:11). 'Though your sins be as scarlet, they shall be as white as snow,' declared the Lord (Isa. 1:18). However, the blood of Christ will have no cleansing effect upon the wicked, for the stain of sin shall remain on their garments (D&C 29:17)." (Hoyt W. Brewster, Jr., Doctrine and Covenants Encyclopedia, p. 195-6)
Orson Pratt
"'…he shall purify the sons of Levi and purge them as gold and silver, that they may offer unto the Lord an offering in righteousness.' That same fire will rest upon the abodes of those that come into that temple, and they will be filled with fire and the Holy Ghost. They will be purged of all iniquity, and every ordinance that will be administered in that temple will be administered by holy hands, and you will understand and know the meaning thereof…The Lord will reveal these things in their day; he will reveal everything that is needful, so that the knowledge of God may rest upon you, and that there may be no darkness with you. Amen." (Journal of Discourses, 21:331)