I’ll Just Sit Over Here, ThanksBy Rabbi Jack Abramowitz
Next, G-d told Moshe about the various genital discharges that men and women might have. (Please be advised that, for the sake of clarity, we’re not going to euphemize here.)
If a man has a pus-like discharge from his penis, it can make him unclean. It does so if it drips for a significant period of time (in the case of a thin discharge) or if it sticks to the penis (which is a thicker discharge – this may mean that the discharge clogs the urethral opening – see Talmud Niddah 43b). In either of these cases, the person is ritually unclean and he renders unclean any bed he lies on or any object he sits on. Such a person is called a zav.
Anyone who touches a zav’s bed or sits on something the zav had been sitting on becomes unclean. He must immerse himself and his clothes in a mikvah, remaining unclean until nightfall. The same is true if he touched the zav or his saliva. The saddle a zav rides on also transmits this uncleanliness; a person must immerse himself if he touches it and also his clothes if he lifted or carried it.
The zav will remain perpetually unclean, and will transmit this uncleanliness to others, until such time as he completely immerses in a mikvah. If the zav touches the interior of an earthenware vessel, it must be broken, but a wooden vessel can be immersed.
After the zav is healed of his discharge, he must wait seven days, then immerse himself and his clothes in a mikvah. On the eighth day, he must bring two birds, one as a sin offering and one as a burnt offering. After that, he’s all clean.