I've seen some " weird " toilet plumbing in RVs ; undersize pipe from the toilet to the tank 2" , too many sharp turns ( 90 degrees) , and a 6' to 8' run to the black tank with virtually no slope. All to make the " designers ideal " floor plan work . Lots of layouts that require a plunger or a snake ; often .
I'll take my 3" pipe with 2 , 22.5 degree fittings over the 15" drop to the tank any day . Floor plan might be what some consider awkward , but it works for us.