72 Pa. Stat. § 5574
All penalties and interest imposed on unpaid delinquent city taxes in cities of the first and second class, on unpaid delinquent school taxes in school districts of the first class and on unpaid delinquent poll, poor district, institution district and county taxes in counties of the second class for the tax year one thousand nine hundred and thirty-nine and all previous years, assessed and levied against any parcel or parcels of real estate, are hereby abated without the necessity of further action by the authority levying the tax unless such authority rejects the provisions of this act within thirty (30) days after the effective date hereof, if said delinquent taxes are paid as hereinafter provided.
In order to receive the benefits of the installment system of payment provided by this act, at least twenty per centum of the unpaid delinquent taxes due for the year one thousand nine hundred and thirty-nine and for all previous years shall be paid on or before the first day of November, one thousand nine hundred and forty-one, and each year thereafter a payment shall be made in such an amount that on or before November first, one thousand nine hundred and forty-two, at least forty per centum of such taxes shall have been paid, and that on or before November first, one thousand nine hundred and forty-three, at least sixty per centum of such taxes shall have been paid, and that on or before November first, one thousand nine hundred and forty-four, at least eighty per centum of such taxes shall have been paid, and that on or before November first, one thousand nine hundred and forty-five, the final payment of the entire balance due on such taxes shall have been paid: Provided, however, That if during any such installment period a taxpayer or owner desires to pay either more or less than twenty per centum of the said unpaid delinquent taxes he shall be required, subject to the above limitations, to pay all said taxes on such parcel or parcels of real estate levied for any one or more years, or any balance unpaid and owing for such year or years, at the time of such payment: And, provided further, That the taxes on such parcel or parcels of real estate levied for the year one thousand nine hundred and forty-one, together with any interest and penalty due thereon, shall be paid on or before the first day of November, one thousand nine hundred and forty-one: And, provided further, That the respective current taxes on such parcel or parcels of real estate levied for the years subsequent to the year one thousand nine hundred and forty-one during such installment periods assessed and levied by such taxing authority shall be paid before they become delinquent. For the purpose of this act a tax shall be deemed to become delinquent on the date when a penalty attaches to the tax. If, and whenever, any of the said current taxes, or any of the said installments, are not paid when due and payable as herein provided, then, and in that event, there shall become due and payable for such year a sum equal to one-fifth of the total amount of the abated penalties and interests in addition to the other payment required to be paid under this act during that year, which delinquent payment and said additional sum shall be payable and must be paid at the time the next succeeding installment payment becomes due under this act. If such sum is not so paid, then the total amount of the abated penalties and interest, less the aggregate of any such additional sums theretofore paid, shall be revived and added to the unpaid taxes with the same force and effect as if such abated penalties and interest or portion thereof had never been abated and the taxpayer shall not thereafter be entitled to any further benefits or privileges under this act.
72 P.S. § 5574