Hi Dave, any correctly qualified assessor will assess you to exactly the same standard for any vehicle whether it’s a tanker or a curtainsider. I presume you have told them you have not driven tankers before but they will still expect you to drive to a decent safe standard.Don’t worry about that just try to be smooth and brake early and progressively rather than all at the last minute if the vehicle is loaded. Remember not to drive as if you are on a test (as you were probably not at a great standard then) but show them you are confident safe and cautious when nesssecary. Drive to the conditions, stick to speed limits and keep a decent distance from the vehicle in front.
Hope it goes well for you.