This can be done using the A2AFT feature, which combines the CU*BASE auto-funds transfer (AFT) functionality with the A2A feature that allows funds to be transferred to or from an outside FI using ACH. Refer to the booklet below for complete instructions.  Setup is done via Tool #884 Update Auto Transfer Information then Add A2A Out (A2A must be activated for your CU for this feature to appear).

If you choose the "Sweep the entire balance..." option, you can specify the minimum amount to transfer every time, as well as an amount to leave behind in the operating account, and even a transfer increment if you wish.

Keep in mind the scheduling of dates based on ACH business days. If an A2AFT is scheduled to transfer on the last day of the month, if the last day of the month is a non-ACH business day, the transfer may be delayed.

Note: A2AFTs can also be set up to receive funds from an external operating account into a credit union investment savings account,but for these the only option is to specify a standard dollar amount to be transferred every time, because the balance/account which would allow us to create rules on available balance, etc., is not held in CU*BASE.