Pesachim 67B

כי האי גוונא ⁠— זב נמי טמויי מטמי באונס כדרב הונא. דאמר רב הונא: ראיה ראשונה של זב מטמאה באונס.

In a case like this, meaning, if we compare the two cases in this way, a zav also becomes impure through an accident, in accordance with the opinion of Rav Huna, for Rav Huna said: The first sighting of a zav establishes ritual impurity even through an accident. In order to contract the more severe ritual impurity of a zav that lasts 7 days, a man must experience at least two zav discharges. If he has only a single discharge, he contracts a less severe ritual impurity that lasts until evening, like one who experienced a seminal emission. This first discharge establishes impurity even if it results from some accident, and no effort is made to attribute it to some other factor.

מאי חומריה דמצורע מזב? שכן טעון פריעה ופרימה, ואסור בתשמיש המטה. אדרבה זב חמור, שכן מטמא משכב ומושב, ומטמא כלי חרס בהיסט.

The Talmud asks further: What is the stringency of a metzora over a zav? That a confirmed metzora is required to let his hair grow and rend his garments and he is prohibited from marital sex, none of which applies to a zav. But on the contrary, there is room to say that the legal status of a zav is more severe, for a zav imparts ritual impurity to that upon which he lies or sits even if he does not come into direct contact with it, and he imparts ritual impurity to an earthenware vessel through movement. If he causes an earthenware vessel to move, it becomes ritually impure even if he touches it on the outside, and even if he does not touch the vessel at all. Ordinarily, an earthenware vessel becomes impure only through contact on the inside of the vessel.