Our 97 35' has always had a bad obor in the rear closet and the head is usually stinky also. I finally roused myself into action and discovered that the knuckleheads had placed the holding tank vent right at roof top level, just aft of the head's vent hood. This leads to fumes entering the head unless you kept the vent hood closed. Also, the hole in the roof for the 1.5" pvc vent pipe is about 1/2" larger than the pipe and is NOT sealed to the pipe. This allows fumes to enter the rear closet.

I removed the vent cover and installed a 2 foot section of 1.5" pvc ELECTRICAL CONDUIT not pvc sch 40 plumbing pipe. The conduit has the female joint already formed in one end. BEWARE !!! The existing vent pipe is NOT permenently attached to the holding tank. Whatever you do, DO NOT , put any upward pressure on it. I shortened the female joint on the conduit so that there is only about 2" to slip over the existing pipe. I also sanded the interior of the joint to slightly decrease the tightness of the fit.

Before installing the conduit you need to drill a couple of rows of holes in the top to allow air flow. I capped the top with a 2" cap from the plumbing section of HD. Currently my cap is just sitting on top of the conduit bit I have several ideas about permenently mounting it. I remounted the original vent cap back to the roof [ unfortunately the vent cap was not centered from the factory so I had to drill new mounting holes and fill the old ones ]. In the plumbing section you will find a rubber 1.5" to 2" pipe adaptor. This is a good fit on the conduit and the 2" section will barely fit the top of the vent cap _base_. Discard the original, removeable cap. Clean up the _base_ good and use some quality sealer when screwing back to the roof.

I used grease to help the conduit slide easily over the original vent pipe and some more grease to slide the rubber adaptor down over the conduit. Do not clamp the 2" end of the adaptor. Do not force the rubber adaptor too far down over the vent cap _base_ or the conduit may be lifted up off the vent pipe. I used some 1" strap aluminium to make a brace from the roof rail over to the new, taller vent. A hose clamp is fine for attaching the brace to the conduit.

Matls:

1.5" x 10' Elec pvc <$5.00

1.5" to 2" rubber adaptor <$5.00

2" PVC cap <$2.00

1"x1/8" x 4' alum strap < $9.00

SS hose clamp , 3/16" pop rivets - in the garage.

I can send pics if interested.