Repairing a Grey Water Tank
Dave and Helen Damouth www.damouth.com
March 27, 1999
While in Mexico, we drove with fairly full sewage tanks from a boondocking site, over rough roads, and over quite a few of the typical high Mexican speed bumps called "topes". The stress was too much for our grey water tank, which ripped out all its mounting screws, and fell down to the highway. We didn't notice immediately, and dragged it down the highway for many miles.
The tank remained attached, held in place by the drain pipe on the street side which was fortuitously mounted and supported in a position so that it didn't break when the tank fell, and held the rear streetside corner of the tank firmly attached in nearly its original position. The curbside forward corner of the tank dragged along the road until it wore a hole through the tank, draining the water, relieving the weight, and allowing the tank to spring back slightly upwards so that it was no longer touching the highway.
When I discovered the problem, I was able to support the tank temporarily with rope. This tank is located between the two trailer axles, so I could tie rope to the axles, looping under the tank. With this temporary support, I was able to continue driving until we were back in the United States. Fortunately, this was the last day of our trip, and we were already on our way to the border when the problem occurred.
After settling in to a pleasant modem-friendly campground with no rules against mechanical repairs (we expected to be there a while) I crawled under the trailer, removed about a zillion sheet metal screws to dispose of the shreds of the plastic center section of the underbody panel, and surveyed the damage.
The center section of the underbody cover of the trailer was broken and shredded, where the heavy tank dropped on to it and forced it down to the road. The whole section of underbody cover will have to be replaced.
The tank has an inch-wide flange around the top edge. It was attached to the trailer floor with wood screws, spaced about every 5" around the flange. The trailer is lightweight stressed-skin foam-core construction. The floor is about 1.5" of foam, with 1/4" plywood on the underside and somewhat thicker plywood on top. So these screws were driven only in to 1/4" plywood. This seems rather marginal for supporting 40 gallons (320 pounds) of water on a bumpy road. I'm not surprised the screws ripped out. It's amazing that they lasted 10 years.
The vent pipe attached to the tank on the top surface, near the front curbside corner, had ripped out of the tank, taking a piece of the tank with it. The hole is ragged, about six inches in diameter, with a few cracks radiating out further. This vent pipe runs up through a wardrobe closet, completely accessible for repair. I hacksawed it off, a couple of inches up from the trailer floor.
One lower corner of the tank had been abraded away. The open area was up to an inch wide and extended about 8 inches along the edge of the tank.
The drain pipe, near the bottom of the tank on the rear streetside corner, seems intact.
The inlet pipes aren't visible – From the inside of the trailer, I can tell that there are two pipes on top of the tank near the street side. The tank is still held up close to the trailer floor on that side. I can't see anything useful about the condition of the top of the tank in that area.
I'll hope that the inlet pipe is still attached properly and that the tank isn't cracked in that area, since that portion of the tank didn't move a great deal and both the top of the tank and the plastic pipes are somewhat flexible.
My initial impression was that the tank was a total loss. But after browsing a couple of catalogs, I guessed that a suitable replacement tank would have to be custom ordered, and probably custom manufactured (probably taking weeks), and the task of precisely locating and cutting holes and mounting the flanges for reattaching the pipes would be fairly major.
Also, one of the pipes entering the tank is located between the bathtub and the wall separating the bathroom from the hallway. The other was centered directly under the bathtub, with almost no clearance for access. I could barely reach these two pipes lying on my belly reaching through a small access hatch, with my arm bent at an awkward angle. I initially thought that I'd have to dismantle the bathroom, remove the interior wall, remove the molded shower enclosure above the full-sized tub, and remove the tub, in order to get enough access to cut and reattach these pipes. Like most plastic plumbing, most of the joints are all permanently glued together, requiring that the pipes be sawed apart and reattached with new fittings.
This provided a strong incentive to hope that this portion of the tank wasn't damaged. It appeared that I could reach all the visible damage without fully removing the tank. I decided to attempt a repair of the problems I could see. The next issue was how to reattach the vent pipe, which was 1.5" black ABS plastic.
After gathering the above information, I quit for the day and spent some time thinking. The next morning, was spent browsing in local plumbing, building supply, and hardware stores:
I found a huge well-stocked hardware store in Harlingen Texas, only a few miles from our campground. This kind of store is now rare, anywhere in the country, and finding one near the campground was an incredible bit of luck. In the plumbing section, I re-discovered a potential solution to the problem of reattaching the plastic with limited access space. Flexible neoprene pipe couplers are made in sizes to fit these pipes (and most other sizes of drain pipes). These fittings are simply slipped over the ends of the pipes, and tightened with stainless steel band clamps
In the same hardware store, I looked at several brands of specialized epoxy adhesives, read the data sheets, and talked to an employee who actually seemed to know something about the products (also very rare these days). I chose a product called "SuperMend", distributed by Titan Corp, Lynnwood, WA. It is high viscosity (stays where you put it, in thick layers), high tensile strength (30,000 psi), and is advertised as having good adhesion to ABS plastic (and to lots of other materials as well). It also has a rapid cure time. They also had packages containing a couple of square yards of light fiberglass cloth.
I also bought a package of 100 Robertson-head wood screws for reattaching the tank to the trailer.
They also had a magnetic-chuck extension shaft for my electric drill, and a Robertson bit to fit this chuck, which should allow me to drive the several hundred screws to mount tank and underbody panel without ruining my arm and wrist.
In a building supply store, I found 4' x 8' sheets of thin fiberglass-reinforced plastic white wall paneling. One of these panels seemed adequate for replacing the missing section of underbody covering.
With a little luck, this would be everything I needed to do the task.
I got back to the trailer with enough time to clean up the tank and the ripped out flange, carefully clean and roughen the areas to which I would apply epoxy/fiberglass patches, and do the two repairs.
I cut two layers of fiberglass cloth and verified it would drape neatly around the abraded corner and edge of the tank. I mixed a batch of epoxy, buttered up that area of the tank, pressed the two layers of cloth into the epoxy, and added another layer of epoxy over the top.
It was a challenge to get this done before the epoxy got hot and began to harden. The "rapid cure" feature has turned out to be a disadvantage in the 90-degree weather we've been having in Harlingen, and I only had about five minutes of working time for each batch.
I cut more fiberglass to fit over the damaged top vent attachment, extending well out on to the flat tank surface, and up over the flange that had been ripped out. I mixed another batch of epoxy and did a similar repair, applying the epoxy quite thickly to reinforce this area.
Next morning, I tested the adhesion by trying to pry loose isolated bits of epoxy around the edges of the patch. It seems very well attached. This repair might actually work!
I then propped the tank back into position with pieces of wood and a few temporary screws, reattached the vent pipe with the neoprene coupling, closed the grey water valve, and turned on the water in the sink to fill the tank. All went well until the tank was nearly full. The bottom patch doesn't leak. But as soon as the tank was full, water began cascading out from around the top of the tank! So much for optimism.
After draining the tank, I did what I should have done in the first place:
I hacksawed the drain pipe.
I detached my new vent pipe coupling
I detached the wires to the tank water level sensors.
I found that I could fit, lying on my belly reaching in through a small access hatch, a bare hacksaw blade in to cut the two inlet pipes under the tub. Wrapping one end of the blade with duct tape allowed me to saw fairly neatly through both pipes, with considerably pain and sweat.
Now, I could remove the remaining few screws on the street side, remove my temporary props, and lower the tank to the ground, allowing me to see the additional damage:
The two inlet pipes attached to the tank had ripped out of the tank, taking a piece of the tank with them. The holes were ragged, about six inches in diameter, with a few cracks radiating out further.
Back to the hardware store! I bought three more neoprene coupling (these pipes are 2"), and a lot more epoxy.
After drying, cleaning, and roughening the areas to be repaired, I did the additional fiberglass/epoxy patches. I applied some more epoxy to the vent flange repair, seeing that since I couldn't fully see what I was doing during this previous repair (with the tank still in the trailer), I hadn't gotten really complete coverage in a couple of areas. This used up another day, and I allowed the new patches to cure overnight.
Next morning, I re-installed the tank. Because of where I had to saw one of the inlet pipes, it had a 45 degree elbow and a few extra inches of pipe attached. To get this back up through the floor, I had to substantially enlarge the existing hole in the floor of the trailer. Lacking my big Sawzall reciprocating saw (which is sitting back east in my storage locker) this was an unpleasant task, done by drilling a row of 1" holes and sawing between them with the loose hacksaw blade. Once the hole was cut, the tank slid easily into place. I propped it up temporarily, put in a few screws, and then verified that each of the four neoprene pipe couplings could be slid into place, and that the screws on the band clamps were all accessible with a long screwdriver.
At that point, I crossed my fingers, declared the repairs finished, and started re-installing the many screws. The electric drill and extension chuck was a lifesaver. I spaced the new screws somewhat closer than the originals, so that the tank support should now be better than before. It required considerable care not to strip the threads in the flimsy 1/4" plywood by overtightening the screws.
After getting all these screws installed, positioning and tightening the band clamps, reattaching the sensor wires, it was time for another pressure test. I filled the tank, and then filled the bathtub, with the drain open, providing considerably more pressure than the tank would ever experience in use.
With this pressure, the bottom of the tank bulged a bit, and drips appeared at a stress crack, in the middle of a reinforcing corrugation molded into the bottom of the tank. This crack may have existed for some time - I see no reason for it to be associated with the other damage.
So: drain the tank again, dry and prepare the area (fortunately, the drip stopped with the pressure removed), and go through the whole repair process again, fortunately in a nicely accessible area where I don't have to remove the tank.
After the epoxy had cured for an hour or so and wasn't sticky, I began the process of fitting and cutting the new underbody cover to size. This was installed with another zillion small self-tapping screws, driven into new pilot holes drilled in the steel frame flanges and cross members.
By the time this was done, I judged that the last epoxy job had cured long enough. I declared the job done and told Helen she could again use the sink drains. (We had been using our largest cook pot as a temporary sink, emptying it into the toilet occasionally.
In total, the task took five days of head-scratching, shopping, and labor. The major costs were about $20 for the new plastic panel, $37 for the epoxy (five packages of about 4 oz. each – it would have been a lot cheaper in a bigger package, but it wasn't available that way locally), and a few dollars for the pipe fittings, screws, sandpaper, solvent, etc.
As I write this, it has been three weeks since the repair was completed, and the tank and plumbing are still watertight. We haven't traveled over bumpy roads with full tanks (the real test) but I hope never to do that again – at least not for a great distance.