Here Jesus speaks about "bathed" and "wash" and "clean" to mean making someone spiritually clean or pure. Since Jesus said in 13:7 that the disciples would not fully understand what was happening, translations should keep the "washing" imagery and not try to explain it in the text.
The word "but" shows the contrast between a person needing to be cleaned and a person already being being clean. In some languages "but" would not be used. Alternate translation: "He who is bathed has no need, except to wash his feet, because he is completely clean" or "He who is bathed has no need, except to wash his feet; he is completely clean" (See: [[rc://en/ta/man/jit/writing-connectingwords]])
This double negative emphasizes that to wash the feet is the only thing that he who is bathed needs. Alternate translation: "He who is bathed needs only to wash his feet" or "The only thing a person who has bathed needs is to wash his feet" (See: [[rc://en/ta/man/jit/figs-doublenegatives]])
It is implied that this need concerns washing the whole body. Alternate translation: "has no need to be fully bathed" or "does not need me to wash his whole body" (See: [[rc://en/ta/man/jit/figs-explicit]])