On or before the day fixed for his appearance the defendant may appear and answer. The defendant in his answer may assert any legal or equitable defense or set-off arising out of the tenancy. If the complaint alleges that the tenancy should be terminated because the defendant tenant, subtenant, sublessee, or resident engaged in drug-related activity, or allowed any other person to engage in drug-related activity at the rental premises with his or her knowledge or consent, no set-off shall be allowed as a defense to the complaint.