53 Pa. Stat. § 17054
In all actions, if the constable, sheriff, or other officer, to whom any writ of summons, or other original writ is directed, shall return "nihil" endorsed thereon, it shall and may be lawful for the said county treasurer to sue out an alias writ, and thereupon, if the said constable, sheriff, or other officer, shall make return of the said alias writ, with "nihil" endorsed thereon, the said return of two "nihils" shall be in all respects equivalent to actual service of the same, as is now the practice in cases in scire facias on judgments and mortgages: Provided however, that it shall be the duty of the said constable, sheriff, or other officer, to give notice of the said alias writ, by serving a copy thereof on the tenant in possession of the premises described in the said register, if any, or if there be no such tenant, by posting a copy of the same in some conspicuous part of the premises, at least ten days previous to the return thereof, and also by publication in one or more newspapers of the city of Philadelphia, which publication shall recite the amount of tax claimed, and the description of the real estate as set forth in said registry.
53 P.S. § 17054