A purchaser of alternative fuel, other than a bulk user of alternative fuel or a retailer of alternative fuel who is liable for the tax pursuant to subsection A of § 58.1-2251, shall remit the tax due on the fuel to the provider of the fuel. A bulk user of alternative fuel or retailer of alternative fuel who has posted a bond in accordance with § 58.1-2246 shall not be required to remit the tax to the provider until the date the provider is required to pay the tax to the Commonwealth. All tax payments received by a provider of alternative fuel from a bulk user of alternative fuel or retailer of alternative fuel shall be held in trust by the provider until the provider remits the tax payments to the Commonwealth, and the provider shall constitute the trustee for such tax payments. The date by which other purchasers of alternative fuel are required to remit tax to a provider shall be determined by agreement between the provider and the purchaser.