Debt Buy-Down Act This bill amends the Internal Revenue Code to allow individual taxpayers to designate up to 10% of their adjusted income tax liability for the reduction of the public debt. The bill also establishes in the Treasury a Public Debt Reduction Trust Fund to hold tax revenues generated by this bill for the reduction of the public debt. The bill amends the Balanced Budget and Emergency Deficit Control Act of 1985 to: (1) require spending to be reduced annually by an amount equivalent to the revenue generated by this bill, and (2) enforce the requirement for spending reductions using a sequestration, with exemptions for Social Security retirement benefits, veterans benefits, and net interest payments on the debt. (Sequestration is a process of automatic, usually across-the-board spending reductions under which budgetary resources are permanently cancelled to enforce specific budget policy goals.)