If you look on page 3 of the attachment you will see there are two anti-syphon vents, one for each tank on your 36FL. These are located inside the cabinets near the sinks or close by. They are spring loaded diaphragms that let additional air into the lines when draining the tanks (suction), and then they are "supposed" to close when the suction stops. If they don't close, the smell comes into the coach.
Check the one in the bathroom, it may have failed. They just unscrew off the top of the vent stack.
Here is some info on them:
Anti-Siphon Trap Vent Devices (ASTVD)
Another type of vent is the anti-siphon trap vent device. These handy gadgets are used as a secondary vent to aid in draining sink fixtures. Also called “check vents,” ASTVDs allow air into the drainage system, but prohibit air from passing out of the system. ASTVDs are installed in the liquid drain piping system, at or near a P-trap inside a cabinet. Look under the kitchen and lavatory sink area and you should find them. They are mounted at least 6-inches above the P-trap’s horizontal arm. ASTVDs do not allow odors to escape into the living portion of the RV because of an integral atmospheric pressure-controlled, rubberized, one-way valve. In other words, air in, but not out.
In addition to ASTVDs, there must still be at least one vent protruding through the roof to allow sewer gases out of that holding tank; ASTVDs are not primary vents. The better-designed waste systems will have ASTVDs installed at every P-trap as well as a direct vent running from each holding tank up and through the roof. Remember though, with the advent of the HepvO waterless sanitary valve, ASTVDs are not required. With the HepvO, eliminating the ASTVD and the P-trap should result in more cubic inches of storage space under every sink. During manufacture, coach makers can eliminate the cost of P-traps, ASTVDs (and their associated fittings, tee’s and piping), as well as shower-mounted skylights, besides gaining the extra storage space.
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