72 Pa. Stat. § 5971j
It shall be the duty of the purchaser or purchasers at this treasurer's sale, as soon as the property is struck down, to pay (i) the amount of the purchase money, or (ii) such part thereof as may be necessary to pay all taxes, except such taxes as have heretofore been filed as liens in the office of the prothonotary, and all interest, and costs, and also one dollar and fifty cents for the use of the prothonotary for entering the report of the treasurer and acknowledgment of the treasurer's deed, as hereinafter mentioned, plus an additional amount equal to twenty-five per centum of the purchase money. In case said amount is not forthwith paid after the property is struck down, the sale shall be avoided and the property immediately put up again by the said treasurer. In the event the purchaser fails to later make complete settlement at the time and in the manner provided for in this act, any money paid under the provisions of this section shall be forfeited and shall be disposed of the same as purchase money.
Any such property, for which an amount sufficient to pay such taxes, interest, and the costs is not bid, shall be purchased by the county commissioners, in which event the requirements of the preceding paragraph of this section shall not apply.
72 P.S. § 5971j