How to make StringBuilder empty again in .NET 3.5 ?

I have a loop where i create some string value based on certain conditions. I did place StringBuilder object outside of the loop and each time i have new row in loop i need to clear StringBuilder appended values for this row.

How do i clear those?

        StringBuilder sb = new StringBuilder();

        foreach (DataRow row in recipientsList.Rows)
        {
            sb.Length = 0;
            sb.Append("<ul>");
            if (row["needsToActivate"] == "1")
            {
                sb.AppendFormat("<li>{0}</li>", getUsersWithoutActivationTemplate());
            }
            if (row["needsToEnterSite"] == "1")
            {
                sb.AppendFormat("<li>{0}</li>", getUsersWithoutEnteringWebsiteForTwoWeeksTemplate());
            }
            if (row["needsPicture"] == "1")
            {
                sb.AppendFormat("<li>{0}</li>", getUsersWithoutPicturesTemplate());
            }
            if (row["needsText"] == "1")
            {
                sb.AppendFormat("<li>{0}</li>", getUsersWithoutTextTemplate());
            }
            if (row["needsCharacteristic"] == "1")
            {
                sb.AppendFormat("<li>{0}</li>", getUsersWithoutCharateristicsTemplate());
            }
            if (row["needsHobby"] == "1")
            {
                sb.AppendFormat("<li>{0}</li>", getUsersWithoutHobbiesTemplate());
            }
            sb.Append("</ul>");
}

Code with accepted answer;