I owe the IRS some money (less than 25K) and they've emptied my bank accounts. It was less than the total amount owed, and now I'm worried that when I get my paycheck this month it'll be nearly empty. Is it a sure thing that they'll garnish my check if they didn't get their full due through the bank?

Yes, if you put more money into the bank it is just taken. So don't have the check put into the bank.
*** do expect them to garnish a percent of that check also

But if it goes into the bank, they will just take it all once it hits the bank.
** you will also have issues if there were outstanding checks, not cleared at the bank, they will come back and start bouncing also

QUOTE,"Is it a sure thing that they'll garnish my check if they didn't get their full due through the bank? "--- Suppose the IRS levies your wages, the levy is served on your employer. Your employer will be ordered to pay over a large portion of your paycheck to the IRS until your tax debt is paid. However, the IRS does not take all of your paycheck; they allow you to be paid the standard deduction amountand the personal exemption amount based upon your filing status and number of dependents.
For instance, if your filing status is single with one dependent (yourself), you would be allowed to keep $8,450 for the year of 2010. The amount that you earn, above and beyond these amounts, must be paid over by your employer to the IRS.