Midrash su Levitico 14:46

This is the source for the sages' gradations of partitions (mechitzoth). Wherever zav confers tumah, metzora (leper) confers tumah. metzora is of greater stringency (than zav) in that it confers tumah upon one who enters (a house afflicted with tzara'ath [viz. Vayikra 14:46] [— wherefore a metzora is sent out of all three camps]). Wherever tamei meth confers tumah, zav confers tumah. zav is of greater stringency (than tamei meth) in that it confers tumah under an even mesama (a stone beneath which there is a cavity [viz. Vayikra 15:9] [— wherefore a zav is sent out of two camps]). Wherever tvul yom (one who has immersed in the daytime [pending purification in the evening]) confers tumah, tamei meth confers tumah. tamei meth is of greater stringency (than tvul yom) in that it confers tumah upon a man (who touches him, viz. [Bamidbar 19:22] [— wherefore a tamei meth is sent out of one camp]). Wherever one's lacking atonement (through an offering) renders (him) unfit (for eating consecrated food) tvul yom renders (him) unfit. tvul yom is of greater stringency (than one's lacking atonement) in that he renders terumah unfit.

4) (Vayikra 14:46) ("And he who comes into the house all the days that he has shut it up shall be unclean until the evening.") "And he who comes into the house": when he enters — his head and the greater part of his body. "the days that he has shut it up": and not the days that he peeled its plague-spot (i.e., If he peeled its plague-spot within the days of its quarantine and threw (its peelings) out [even though he thereby transgressed a negative commandment], one who enters does not become tamei.) I might think that I (also) exclude (from tumah one who enters) a confirmed (plague-spot house) whose plague-spot was peeled; it is, therefore, written "all the days" (to include such a contingency).

5) "and he shall be unclean until the evening": We are hereby taught that his clothes do not become tamei. I might think (that this is so) even if he remained there long enough to eat a p'ras (a half-loaf); it is, therefore, written (in the following verse) "and he who eats in the house shall wash his clothes."