Prevent XmlSerializer from formatting output

Not very intuitive, but the Indent property on the XmlWriterSettings controls the whole formatting:

var serializer = new XmlSerializer(typeof(MyClass));

using (var writer = new StreamWriter("file.path"))
using (var xmlWriter = XmlWriter.Create(writer, new XmlWriterSettings { Indent = false }))
{
    serializer.Serialize(xmlWriter, myObject);
}

There are a few more options on XmlWriterSettings that you might want to explore.