&gt; <i>in particular insisting that they couldn&#x27;t require the diesel exhaust fluid tank to be topped up by the end user</i><p>Not being rude, but I&#x27;m having trouble parsing that part of your comment.<p>Do you mean that the US authorities won&#x27;t let diesel car owners re-fill the diesel exhaust fluid tank by themselves, i.e. the re-fill must be performed by a dealer?<p>Also is the DEF tank just a US thing? I&#x27;d never heard it before (UK resident here).