72 Pa. Stat. § 5572.10
Any taxpayer who, on the effective date of this act, is making payments on delinquent taxes under any of the acts referred to in section eight, and any taxpayer who has made any payment or payments under any of the said acts, or any taxpayer who avails himself of the privilege of this act, shall be permitted to pay to the county treasurer or receiver of taxes, and the county treasurer or receiver of taxes shall receive, at any time during the year, amounts less than twenty per centum of the total amount due and payable under this act or any act referred to under section eight: Provided, however, That the total payments made in any one year shall be equal to or in excess of the total amount due on any one contract or agreement to the county treasurer or receiver of taxes under the terms and provisions of this act.
72 P.S. § 5572.10