In this week’s continuation of the holding tank odor article, some insight into what may be causing persistent odors and some preliminary checks you can perform will be provided. Read on if you have performed the basic steps in part 1 but you are still experiencing holding tank odor.
If your RV has an underbelly, common in many trailers, you should drop a section of it near the holding tank and check for moisture or odor. There are two main types of underbelly, these being thick laminated sheets that are screwed into the frame, and the thinner Dicor tape that is wrapped around the frame during manufacture of the coach. If your underbelly is the first type, simply remove some of the screws in the region of the holding tank valves and pull down that section of the underbelly. If you have the Dicor tape, you will have to cut part of the underbelly, being sure not to remove a section entirely. Once you are finished, you will have to purchase Dicor strip tape and tape the underbelly back up. This can be a difficult process, especially if there is no blocking above the area you are cutting. Therefore, be sure you are willing to commit to the inspection process prior to starting.
Note that there may or may not be fiberglass insulation above the underbelly. Using a flashlight and your hand, inspect and feel the area above the underbelly for moisture, stains, etc. One obvious telltale sign will be water on the top surface of the underbelly itself. If you detect any moisture, it is imperative that the source of the water be located and repaired. Once the leak has been fixed, the underbelly area should be completely dried. If there is wet insulation in the underbelly, it must be removed and replaced with new insulation.
The most likely source of a leak will be plumbing joints such as the tank and pipe fittings. If you are unable to locate the source of the leak, you can either expand the search area by removing more of the underbelly, or have it investigated by a professional RV shop, as indicated above.
Once, while training a new RV tech, I discovered a leak in the holding tank of a brand new motorhome. The source of the leak turned out to be three small holes drilled in the top of the tank. The holes were inadvertently punched through the tank as a result of floor drillings during manufacture of the coach. 
Since the holes were in the very top of the tank, they would have been hard to detect had we not performed a thorough pre-delivery inspection (PDI). We had to remove and replace the black water holding tank. I often tell technicians about this event when discussing the importance of thorough PDI work. But it’s also a reminder for owners to make sure that both used and new coaches are properly inspected and maintained.
Most RVers are aware of coach damage that can occur as a result of either rain entering the exterior seals or fresh water leaking into the interior of the coach. However, owners should also be aware that waste and drain leaks can also do damage to floors, insulation, chassis, and the like. These leaks often go undetected for some time.
About the Author:
Steve Froese, an avid RV owner, traveler, and Coach-Net member since 2013, is the principal of “A Word to the Wise Technical Communications”, a published RV author, certified RV technician, and licensed Professional Engineer. He frequently collaborates with the “RV Doctor”, Gary Bunzer, and has worked with the RVIA/RVDA as a technical and training writer and consultant. Professionally, he works as a quality engineer and musician. Watch for more of Steve’s work in upcoming Coach-Net publications.
