When such nuisance has been found to exist, and the owner or agent of the building wherein or ground whereon the nuisance has been found to exist was not a party to such proceeding and did not appear in such proceeding, a penalty of not more than three hundred dollars shall be imposed upon any person found to be responsible for the conduct of such nuisance or upon the property. Before such penalty is enforced against such property, the owner or agent thereof shall have appeared therein or shall have been served with a summons and the provisions of the laws relating to the service of civil process shall apply to the service of process. Any person in whose name any real estate affected by any such action stands on the books of the assessors for purposes of taxation shall be presumed to be an owner thereof and, in case of any unknown persons having or claiming any ownership, right, title or interest in property affected by any such action, such unknown persons may be made parties to the action by designating them in the summons and complaint as “all other persons unknown claiming any ownership, right, title or interest in the property affected by this action”, and service may be made by publishing such summons in the manner prescribed in § 52-68. Any person having or claiming such ownership, right, title or interest, and any owner or agent on behalf of himself and such owner, may make, serve and file an answer therein within twenty days after such service and have a trial of his rights in the premises by the court, and, if such cause has already proceeded to trial or to judgment, the court shall fix a time and place for such further trial and shall modify, add to or confirm any finding or judgment as the case requires.