How To Diagnose And Fix Leaky Tank Issues On RV’s
RV’s have got a lot of tanks. There are fresh water tanks, black water tanks, fuel tanks, propane tanks, etc. Many of these tanks are made of plastic and most will last the life of the RV. These tanks also sometimes have valves, and all of them have supply lines, fittings, and brackets that help them mount to the chassis. Occasionally you might discover that you have a leak and leaking tanks need immediate repair. Here are some things you should consider
Diagnosing the leak
As with any type of leak, diagnosis is the first step. Try parking the RV on a surface that will make it easy to see evidence of the leak location such as a concrete pad or driveway. Parking on dirt, gravel or other type of natural surface will not allow the leak location to be so obvious. Some leaks take days to manifest themselves, while other more severe leaks can show signs in minutes.
After you pinpoint the approximate location, try and crawl under the rig (or if you can’t physically do it, see if an RV neighbor friend or relative can for you) and use a mirror and a flashlight to see the top of the tank, though that is entirely dependent on the exact installation on your model of coach. In some instances, frame members may impede your view, or the tank may be positioned flat against the under-flooring.
If it is not a fuel tank, first drain and flush the tank numerous times and then begin filling the tank with fresh water. A garden hose into the toilet will probably be the quickest method if you suspect that your black water tank is the leaker. As the tank nears capacity, closely look with that mirror and flashlight to see exactly where the leak appears first. It’s common to see cracks on the sides of the tank near the top, however there are instances where cracks are on the very top of the tank. Ion a black water tank, it could simply be leaking from around the 3-inch pipe from the toilet or the smaller vent pipe requiring nothing more than new sealant.
If a vent pipe were to drop it usually drops into the tank through a rubber tank fitting. This may or may not cause an actual tank leak. You can check the vent pipe from up on the roof. Remove the sewer cap for that vent line and look for the ABS pipe. It should stick up about an inch above the roof. If it is much lower than the roof line or not visible at all, then it may have indeed dropped into the tank.
If it’s not possible to view the top portion of the holding tank from below the motorhome, then the tank will have to be dropped. This may involve removing hangars or angle brackets but it’s not a difficult task though it is time consuming to remove.
On a black water tank, remove the toilet and the floor flange and the vent pipe that extends up through the roof. You might have to cut the ABS vent pipe close to the floor line and use a coupler fitting after reinstallation. You must also remove the 3-inch tank outlet fitting and disassemble the termination assembly. After the tank has been removed, reinstall the closed termination valve to block the outlet, support the tank and refill it while on the ground. At that point it will be obvious evident where the leak exists, or you might even be able to see the crack with your eye without having to fill it.
How to repair a leaky RV holding tank
At our shop, we employ a plastic welding machine, but not all repair shops are equipped with a plastic welder so you may have to shop around. We strongly recommend against using an aftermarket patch kit as the only long term and proper method of repairing cracks in plastic tanks is by welding. Patch kits should only be used in an emergency situation or for a temporary fix.
If the tank is damaged from some collision damage, or perhaps you ran something over, then you might have to replace the entire tank.