72 Pa. Stat. § 6091
If the owner or owners of lands sold as aforesaid, shall make, or cause to be made, within two years after such sale, an offer or legal tender of the amount of the taxes for which the said lands were sold, and the costs, together with the additional sum of fifteen per cent. on the same, to the county treasurer, who is hereby authorized and required to receive and receipt for the same, and to pay it over to the said purchaser upon demand, and if it shall be refused by the said treasurer, or in case the owner or owners of land so sold, shall have paid the taxes due on them, previously to the sale, then, and in either of these cases, said owner or owners shall be entitled to recover the same by due course of law, but in no other case and on no other plea, shall an action be sustained, and it is hereby declared that so much of the act to which this is a supplement, as requires notice of the taxes being due and sale thereon to be given in certain public newspapers, is repealed, and that no alleged irregularity in the assessment, or in the process or otherwise, shall be construed or taken to affect the title of the purchaser, but the same shall be declared to be good and legal.
72 P.S. § 6091