House Calls with the RV Doctor
By Gary Bunzer
Dear RV Doctor:
I just purchased your book, The RV Owner’s Handbook; thanks for the wealth of information. I own a 27-foot motorhome and am about to embark on the “spring shakedown” and want to recaulk any external caulking that might have cracks or leaks, etc. I note you suggest removing all old caulking, which would be a daunting task in terms of end caps, side molding, roof vents, etc. Can one simply clean the old caulking with denatured alcohol or some other product and then recaulk? How does one tackle such a task?
RV Doctor: Mike, in my opinion, the crucial location where it’s important to remove all remnants of the old sealant is the roof area, specifically the perimeter and any seams. This is especially true if the existing sealant appears to be flaking. For trim moldings, compartment doors, windows, running lamps, etc., it’s not as critical, but aesthetics are important. Take a look at the ugly-looking sealing job pictured here. Even though this awning rail may not leak, it certainly can be made to look a lot better.
On sidewall components, such as windows, for instance, you’ll still want to trim the existing caulking carefully with a razor knife and slant the blade slightly inward to create a small cavity of sorts. Then apply a new bead of silicone or like sealant. Just a small bead is all that’s necessary. Wet your finger and press the new sealant into the cavity you created with the angle of the knife blade. In some cases, I recommend taping off the area to keep any excess sealant that may be pressed out by your finger from spreading too far. If you trim the nozzle of the silicone tube very small, however, it can be done with less preparation.
Neatness isn’t as critical up on the roof. Be sure to work the sealant into all the cracks and crevices. If, however, the old sealant has become brittle and is flaking or peeling off, then it will be necessary to remove all of it and start over.
In those instances, I also would remove the roof vent itself, put fresh butyl tape under the flange, and then secure it to the roof. The same process should be repeated for all components secured to the roof. And keep in mind that the type of roof (aluminum, fiberglass, EPDM, etc.) will dictate other specific guidelines.
Dawdling Tank Draining
Dear RV Doctor:
I am having a problem draining the black water holding tank on my coach. After I open the valve, the tank drains normally until it is approximately half empty, and then it stops flowing altogether. However, if I unhook the drain hose, it will continue to drain until almost completely empty. I don’t understand why I have to unhook the drain hose to completely drain the tank, or how to resolve the problem. Any ideas or suggestions?
Falls Church, Virginia
RV Doctor: David, barring any severe blockages inside the holding tank, it is apparent a venting problem exists. As a holding tank drains, air must enter the tank from above. All holding tanks must be vented through the roof of the RV. In some cases, the vent pipe can become dislodged and fall down inside the tank, submerging itself in the contents of the holding tank. This effectively blocks off the vent, thereby prohibiting the venting action of allowing air to enter as you try to empty that tank. This is why it seemingly drains normally if you unhook the drain hose. Disconnecting the sewer hose allows air to enter the tank.
Here’s an analogy: Place a drinking straw into a glass of water. If you simply lift the straw out of the glass, the water inside the straw drains out as you lift. Now place your finger over the open end of the straw and lift it out. The water remains trapped inside the straw until you remove your finger from the end.
Liquid entering the holding tank must displace the air when draining into the tank, and air must enter behind the contents during draining of the tank itself. That vent through the roof must work in both directions. Here’s how to check it out. First, have someone depress the toilet pedal. If this allows the fluid to flow, then the vent tube is probably clogged. Climb up on the roof and remove the cover for that holding tank vent. If the ABS piping is not protruding above the roof a couple inches or so, chances are the vent has slipped down into the tank and made contact with the contents. In some cases, you can reattach it correctly from inside the RV; in other cases, the holding tank must be dropped in order to repair that vent connection. A thorough inspection will reveal the best method of repair.
More Water, Please!
Dear RV Doctor:
Like many people, we do a lot of dry camping. And one of the most important resources when dry camping is the water tank capacities. Unfortunately, the new RV we just purchased only has a 50-gallon fresh water storage capacity “” not enough for a long weekend with our three kids. I’ve been told I can add an additional tank to increase that capacity. I’ve even found a site that sells RV water tanks of various sizes at reasonable prices. However, I have no idea how you would go about “linking” the new tank to the existing tank so I would need only one filler spout and one pump. Do you have any suggestions as to how I might do this?
Dear RV Doctor: Dave, installing a second fresh water storage tank is indeed doable; however, I usually recommend a separate fill to accommodate faster filling. It can be done with a single fill by linking the two tanks together using approved fresh water tubing, though both tanks must be on the same level and be the same height in order to get by with one fill spout. You’ll need to connect a water line, the larger the better, at the bottom of each tank and a vent line at the top of each tank, linking the tanks together. Some tanks have auxiliary threaded fittings already installed, but additional fittings can be welded on or spun on by any properly equipped RV shop. There are even two-piece fittings available that simply require a hole drilled in the tank to install.
Leave the pump where it is, and let gravity do the work of equalizing the levels in each tank. Remember, water seeks its own level, so if the tanks are connected together at the top and bottom, they will drain together as water is pumped through the system. They also will fill at the same time, though it may take longer for the levels to equalize during the filling process.
You’ll need only barbed fittings and simple hose clamps, since the new fittings will not be pressurized. Only those fittings located downstream of the water pump will be under any pressure other than static pressure. The hardest part will be routing the fresh water tubing between each tank. But it will indeed provide additional fresh water storage. Don’t forget that the new tank will also require its own drain valve and fitting.
In addition, keep in mind that the coach may need additional black water and gray water holding tanks “” or perhaps you can overcome the extra effluent with a Blue Boy mobile holding tank. You’ll also want to make sure your coach has sufficient payload capacity to add this new tank, and take weight distribution issues into consideration when placing it in the vehicle.