A slang phrase referring to a situation in which an underwriter has successfully sold to investors all of its available issues of a public offering of securities. Also known in more formal terms as "fully subscribed".
Taobiz explains Pot Is Clean
Typically, the goal of a public offering is to price the security issue at the exact price at which all the issued shares can be sold to investors, so there will be neither a shortage nor a surplus of securities. When the pot is clean, the underwriter has no more of the issue to sell to interested investors. If there is still interest in the issue and nothing left for an underwriter to offer, it is probable that the issue was underpriced and oversubscribed.
