Once you are at the police station and provided with an opportunity to take a breath test, you should probably agree to do unless the attorney you consult with advises you otherwise.  The same is true if your case involves an accident and you have been transported to a hospital where it is requested that you provide blood sample. 

In either case, however, the decision about whether or not to provide a sample is a complex one.  In certain limited circumstances, it may be in your best interests to refuse to provide a sample.  This is why it is best to always consult with an experienced Seattle and Washington State DUI attorney before making a decision about whether or not to blow or provide blood.