He wants to get rid of it and replace it with...here it comes..nothing!.
I don't know if you knew this, but the Income Tax doesn't pay for anything other than the National Debt. It doesn't fund schools, hospitals, education, defense, nothing. The Federal Government gets its money primarily from Capital Gains, Exise taxes, social security taxes, bond sales, sales taxes on smokes and booze, taxes designed to "pay" for government programs, etc. The Income tax doesn't fund any function of Government other than paying off the National Debt.
The corresponding reduction in spending on maintaining an overseas empire, useless government departments, and generally vastly reducing the size of government are expected to provide the savings necessary to continue paying off the debt with the elimination of the income tax.