Keep in mind that many TT's FWT is strapped and exposed under the TT while a MH's FWT is often mounted inside supported by the floor. A longer tube is involved and could be run anywhere where they have room for a clean run to the ground. My class C tube ties into the low point drain cold line below my chassis but the petcock is inside a storage compartment.
Sometimes they hide a drain petcock inside a baggage compartment behind a trap door . I have a hinged trap door inside the compartment where the water pump is housed as well as the winterizing valve (pick up tube) . Some rv's also have the fresh water drain petcock in that location .
Other places are below the fridge , there might be a removable panel screwed in place or under the bed near the tank itself.