Re: Citibank and IRS it might be helpful to know that the IRS is typically an account holder like any other account holder at a bank. The FRB/State Bank Charter system exists in a separate realm from the IRS and State Revenue systems. Thusly the bank's custodial roles are separate. Citibank could not in good faith transfer funds from one account holder (the attempted levy target) to another (IRS) without proper justification without Citibank incurring liability. AFAIK the bank simply within the same bank transfers from the target account to the IRS's account along with proper memoranda (particulars) and that is how the IRS gets its money--tax depositaries and such.
Re: $15 service fee. That sounds like a typical inter-institutional transfer fee. However, such is also a typical "service charge".
Perhaps the banks can only issue or multiply clearinghouse credit rather than lawful money.However this leaves your bank in a position where they are earning no money in any of your transactions.