Surely you don't EVER turn a service that has been going for 10 hours around without cleaning? Even Ryanair clean a flight with a tight 20 minute turnaround. Okay, not always perfect but usually pretty good - and certainly better than no cleaning. And we're talking about flights of somewhere nearer 2-3 hours, not 10!
The toilets would always be functional too. For a service like that, the toilets should be refilled with water - and emptied sufficiently elsewhere so they'll never get full in service.
Surely the power cars would need some diesel as well. I'm not sure what the maximum range of a Class 43 is, but I do know that the set off the North Briton has to top up at Aberdeen before heading off to King's Cross. That takes a good ten minutes to do, more if you need to refill the screen wash or something.
I'm not sure if XC trailers have retention tanks, but EC ones consistently run out of water somewhere around Grantham. That's after about five or six hours from Aberdeen or Inverness, so if the loading of the XC service is the same, they need at least one topup at about the half-way point. Trying to start a service with non-functional toilet facilities is probably against some regulation or other (I'm no expert) but perhaps not quite as bad as running out of fuel.