Tax collected but not remitted obliges immediate payment, subject to assessment, interest, and potential equivalent penalty. Tax collected from others but not remitted to the Government is immediately payable by the collector regardless of the supplies' taxability. The proper officer may issue a show cause notice for payment and an equivalent penalty, determine the amount after considering representations, and require payment with interest from collection until payment. A requested hearing must be granted, the officer must record facts and reasons, and issue an order within one year (excluding judicial stay). Amounts paid are adjusted against tax liability and any surplus credited to the Fund or refunded.