(a)  All ordinary expenses incurred in connection with the trust estate or with its administration and management, including regularly recurring taxes assessed against any portion of the principal, water rates, premiums on insurance taken upon the estates of both tenant and remainderman, interest on mortgages on the principal, ordinary repairs, trustees' compensation except commissions computed on principal, compensation of assistants, and court costs and attorneys' and other fees on regular accountings, shall be paid out of income. But such expenses where incurred in disposing of, or as carrying charges on, unproductive estate as defined in section 3312 of this title, shall be paid out of principal, subject to the provisions of subsection (b) of section 3312 of this title.

(b)  All other expenses, including trustee's commissions computed upon principal, costs of investing or reinvesting principal, attorneys' fees and other costs incurred in maintaining or defending any action to protect the trust or the property or assure the title thereof, unless due to the fault or cause of the tenant, and cost of, or assessments for, improvements to property forming part of the principal, shall be paid out of the principal. Any tax levied by any authority, federal, state or foreign, upon profit or gain defined as principal under the terms of subsection (b) of section 3303 of this title shall be paid out of principal, notwithstanding said tax may be denominated a tax upon income by the taxing authority.

(c)  Expenses paid out of income according to subsection (a) of this section which represent regularly recurring charges shall be considered to have accrued from day to day, and shall be apportioned on that basis whenever the right of the tenant begins or ends at some date other than the payment date of the expenses. Where the expenses to be paid out of income are of unusual amount, the trustee may distribute them throughout an entire year or part thereof, or throughout a series of years. After such distribution, where the right of the tenant ends during the period, the expenses shall be apportioned between tenant and remainderman on the basis of such distribution.