Child support payments should be made in accordance with the terms and conditions of the court order. The limitations on wage garnishment are set forth in RCW title 6. (i.e. http://apps.leg.wa.gov/RCW/default.aspx?cite=6.27).
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Look at your Order of Child Support and the Order to pay Maintenance in the Temporary Order. With child support there are two dates: 1st is when the support becomes effective, usually the first day of a particular month. The 2nd is when it is to be paid. Even if it says pay on the first of the month, Office of Child Support will not collect anything until it is past due by, as I recall, 30 days. In the temporary order there is likewise a start date and, in the absence of a specific day for payment, it can be paid any time during the month it is due.
Garnishment is limited. If you do it the employer holds up to 35% of disposable money. If it is a bank or institution they withhold all the money they are holding.
Garnishment is not automatic but wage withholding can be, depending on the Order of Child Support.