(a) If any portion of the claim allowed by the court in a receivership proceeding, or in any proceeding under the Bankruptcy Act (11 U.S.C. chs. 1-14) remains unpaid after the termination of such proceeding, the district director will send notice and demand for payment thereof to the taxpayer. Such unpaid portion with interest as provided in section 6601 may be collected from the taxpayer by levy or proceeding in court within the period of limitation for collection after assessment. For the general rule as to such period of limitation, see section 6502, and for suspension of the running of the period provided in section 6502, see, for example, section 6503. For suspensions under other provisions of law, see, for example, section 11f of the Bankruptcy Act (11 U.S.C. 29(f)). Extension of time for the payment of such unpaid amount may be granted in the same manner and subject to the same provisions and limitations as provided in section 6161(c).

(b) Section 6873 is applicable only where a claim for taxes is allowed in a receivership proceeding or in a proceeding under the Bankruptcy Act. Claims for taxes, interest, additional amounts, or additions to the tax may be collectible in equity or under other provisions of law although no claim was allowed in the proceeding because, for example, such items were not included in a proof of claim filed in the proceeding or no proof of claim was filed. Except in the case of a proceeding under section 77 or chapter X of the Bankruptcy Act, a tax or a liability in respect thereof is not discharged by a proceeding under such act, whether or not a claim is filed in such proceeding, and provisions suspending the running of the period of limitation on the collection of taxes are applicable, whether or not a claim is filed in such proceeding.