Believe all the city hookups have the check valve directly behind the outside connection--very common part, but sometimes very difficult to access. If the hose connection is a round plate with 3 screws,then you could remove the screws and see if there is enough slack to pull the fitting/valve out to get to it. Otherwise, you would get to it from the inside and that can be difficult/tight to reach.
'16 40QBH Phaeton
'15 38RSSA Mobile Suites--traded
'05 36TK3 Mobile Suites--retired but not forgotten