They will use the bank account you have included in your installment agreement. You do not have to write a check. The
IRS usually debit the date you specify when you made the payment. If you
did not select a date, the IRS will withdraw the payment April 18th 2017.
If it is not taken by this time you may want to
call the IRS customer service line at 1-800-829-1040 to inquire
regarding the status.
https://ttlc.intuit.com/replies/3300043
