The tax imposed by this subchapter shall be fully paid and have priority out of the proceeds of any judicial sale of real estate before any other obligation, claim, lien, judgment, estate or costs of the sale and of the writ upon which the sale is made, and the sheriff, or other officer conducting said sale, shall pay the tax imposed out of the first moneys paid to the sheriff or other officer in connection therewith; provided, that if prior to delivery of the deed pursuant to the said sale, the purchaser shall deliver to the sheriff an affidavit as described in § 5409 of this title that the transfer is exempt from tax under § 5401(1)p. of this title, the sheriff shall not pay the tax, but shall deliver the affidavit to the Recorder of Deeds as agent for the Department of Finance.