Saturday, December 9, 2023


Flexible holding tank repair material easy to apply—and it works!

Like many RVers, we suffered through holding tank leaks on a variety of RVs. One memorable occasion, when parked on a slanted post office parking lot, we found the top of our holding tank leaked. Our BLACK water holding tank. Embarrassing, to say the least; difficult to fix, an understatement. We’ve tried all sorts of tank repair nostrums, to a variety of results, usually disappointing. Those that have worked (for our black tank disaster) were complicated and posed major safety issues. Others often just peeled off, or didn’t hold. We’ve now tried a new flexible holding tank repair, and we’re really jazzed.

Dreary dribble issue

flexible holding tank repair material
Minute but prolific. The tiny crack is at arrow point. Pre-prep photo by R&T De Maris

Our current dreary dribble issue made itself known when we were preparing to dump tanks. Under the trailer, a stream about the size of a pencil point was splooshing down on the gravel parking pad. Thank heavens this wasn’t a manifestation of horrifying black water, just the ghastly gray water. Just where the stream started wasn’t clear, as it trailed across the rig’s underbelly. We ended up cutting a large area of the coroplast to find the source. Right there, in a corner, right down at the bottom of the tank, was a minute but prolific crack.

Being “on the road,” there’s never a “good time” for something like this to happen. We were parked at a fairly forgiving relative’s place, so we had some breathing room to get the situation fixed. By dumping the tank we were able to slow the flow; but the issue was, how to fix it?

Some other stuff works—but a lot doesn’t

The last tank repair we undertook was a major issue. A crack along the top of a different rig’s black tank stretched nearly 40” and allowed the flat, thinnish top of the tank to separate from the tank walls. If we overfilled the tank or, in our point of discovery, got off-level, then the contents would spill right out, and into the fiberglass insulation-stuffed belly space. For that repair, we worked with a product called Plasti-Mend. That stuff is a resin substance that melts into the existing plastic, and effects a new repair. It worked great! Trouble is, the stuff emits highly toxic fumes, and requires the user to wear a NIOSH (National Institute for Occupational Safety and Health) approved respirator when anywhere near the stuff. We didn’t have that kind of equipment with us, and visions of trying to apply the stuff overhead just didn’t work.

We’d faced similar “small cracks” in other holding tanks. That was a few years back, and then we’d tried commercially available “holding tank repair kits” that promised stellar results. Their definition of stellar and ours were light-years apart. We needed something that really worked, didn’t require special safety equipment and would be quickly available. We ran into some flexible holding tank repair material we’d never heard of: West System G/flex epoxy. Initially designed for marine use, we found good things reported about it.

“Resist a peel or delamination”

G/flex is a 2-part epoxy. photo.

What sets G/flex apart from other repair potions is its ability to stick to just about any sort of plastic (more on that in a second) and its elasticity after the repair is cured. When your RV is rattling down those bumpy roads, if the repair material doesn’t “give” then something’s gonna give—typically the repair itself.

G/flex, says the manufacturer, is formulated to elongate—up to 30%. When the repair twists, expands, contracts, or vibrates, G/flex hangs on tenaciously. “This helps it,” says West Systems, “resist a peel or delamination from starting.” Well, believe us, we’ve been down the road of peel and delaminations with other tank repair compounds.

G/flex is also suitable for tanks other than ABS, commonly found as black and gray water reservoirs. G/flex will also stick to polyethylene plastic—think fresh water holding tanks. These guys can be a bearcat to repair, but G/flex will work on both LDPE and HDPE materials. Oh, did you say you poked a hole in your fiberglass canoe, your plastic roof carrier, etc.? Look to G/flex.

How we stifled our drizzle—prep work…

Here’s the lowdown on how we used this flexible holding tank repair material to stifle the gray water drizzle in our lives. After we tracked down the actual source of the leak (that little bitty crack in the corner), we cleaned up the mess. We rubbed and scrubbed the holding tank with a cloth and cleaner to expunge the ick that’s associated with gray water. With the tank empty (and drains blocked inside to prevent accidental water intrusion, we prepped the repair site.

West Systems suggests when working with ABS or PVC, that prep work includes using an “appropriate solvent.” They don’t specify what solvent, but we used alcohol. Don’t use a laundered rag, but better to use white paper towels. Why the difference? Rags may leave traces of fabric softener on the repair area, which could create adhesion issues. Follow up with making a better grip surface by sanding with 80-grit sandpaper. Dust off and ensure the area is dry.

While you can purchase large quantities of G/flex, we found that a little more than one “set” of G/flex 655 syringes worked well. Yes, the stuff is an epoxy, and the double one-ounce syringes spit out equal portions of the two-goop poop. A small paper plate with a plastic utensil worked well for the mixing surface. Two minutes of mixing made the G/flex ready to apply. With a pot life of over an hour, you don’t have to be in a big hurry to do the fixing.

… and application

flexible holding tank repair material
We added fiberglass window screen for additional strength. R&T De Maris photo

After we applied a layer of the mixed epoxy onto the repair area, we added a layer of plastic window screen, just for good measure. Working with rubber gloves helps you keep your paddies out of the mess. With the fiberglass in place, we molded a bit more G/flex over the fiberglass.

The cure time is about 7 hours. Sad to say, before our “cure” could be effected, we goofed. A small amount of water got run down the drain. The next day when we put a big amount of water in the tank, we found a tiny drip of water from the repair area. Rats! So we drained the tank, dried everything out, and between what was left of our first ounce of unused G/flex and a bit from a second syringe, we recoated the repair area in earnest. An overnight cure proved all that was required. A refilled tank leaked nary a drop.

2,000-mile test coming up

How will the G/flex repair hold up to the rigors of the road? We’ll be putting it to the test shortly. We have close to 2,000 miles to cover before we return to home base. Will this flexible holding tank repair material prove to be truly flexible and watertight? We’ll report back with our findings.

West System G/flex 655 is sold on Amazon; $19.99 per one-ounce syringe.

Had an experience with fixing a holding tank? We’d love to hear about it. Write us, and include photos if you have them. Use “holding tanks” as the subject line.

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Russ and Tiña De Maris
Russ and Tiña De Maris
Russ and Tiña went from childhood tent camping to RVing in the 1980s when the ground got too hard. They've been tutored in the ways of RVing (and RV repair) by a series of rigs, from truck campers, to a fifth-wheel, and several travel trailers. In addition to writing scores of articles on RVing topics, they've also taught college classes for folks new to RVing. They authored the book, RV Boondocking Basics.



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Cancelproof (@guest_254496)
2 months ago

GFlex is an outstanding product. Great choice to showcase here Russ and Tina.

For solvent choices, MEK if you can get it or Xylene which is more readily available.

I have used GFlex on several boats and now, RV repairs such as roof repairs at screw heads (solar) etc.

Highly recommend.

Neal Davis (@guest_254489)
2 months ago

Thank you for the tip. I hope to never use it. 🙂

Tommy Molnar (@guest_254459)
2 months ago

Almost sounds like JB Weld.

Brad Teubner (@guest_254408)
2 months ago

Why wouldn’t you wait until after the test trip to say how great this stuff is?

Tom (@guest_254332)
2 months ago

West Marine has many boating items that apply equally well to the RV. Generally much better made and durable.

Richard (@guest_254330)
2 months ago

It would seem to me that adding the screen material would make it less flexible, no?

Ran (@guest_254324)
2 months ago

I’ll be patiently waiting to hear how this repair holds up! The second coat is probably a good idea from the start. Especially over the fiberglass matte. Thanks for the tip!

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