53 Pa. Stat. § 30904
It shall be the duty of the purchaser or purchasers at said treasurer's sale, as soon as the property is struck down, to pay the amount of the purchase money and before delivery of deed, all other city taxes, penalties, interest and lien costs, if such purchase money is insufficient for the payment thereof and also one dollar and fifty cents ($1.50) for the use of the prothonotary for entering the report of the treasurer and acknowledgment of the treasurer's deed, as hereinafter mentioned, and in case said amount is not forthwith paid after the property is struck down, the sale may be avoided and the property immediately put up again by the said treasurer: Provided, however, That this section shall not apply when the lands are purchased by said city.
53 P.S. § 30904