Most dealers provide the sewer hose and fresh water hose and the filter should already be in it unless it was bypassed to winterize it.
Here's kinda how it works.
When the unit arrives at the dealer seeing as it's already a "retail sold unit"
When the driver delivers a unit, the dealer inspects it for driver damage, defects and missing items. They then have generally 24 hrs to contact the manufacturer to report problems.
Yours being "retail sold" it will most likely go into the shop immediatly for them to install any items that have to be installed/serviced during dealer prep such as installing batteries, filling the propane tanks, attaching the power cord, putting hoses in one of the storage compartments, fixing any issues they find. Usually they will have the unit hooked to shore power and water to test things.
When you arrive to pick it up they should take you on a walk through to do both the PDI (pre delivery inspection) and an orientation and help you hook up your TV.
Some dealers even have hookups and you can stay for the night to check things out.
Basicly the trailer should be ready for you to just throw your stuff in and go camping as soon as you take delivery of it.