The Mystery of the Sewer Vent Leak by GK

[GrampaKilt]

Read this to the end and wonder!

After winter, I noticed quite a puddle of water behind the toilet of my 14DB. Finding nothing amiss by the usual suspects, I decided on observation. During the next heavy downpour, there it was, trickles of water slithering down the back wall (BTW, thank goodness for Adzel) and after every heavy rain since then. For months, I've examined the roof in that area with the proverbial fine tooth comb. Even tried flooding. Nada! Then today...

I took the cover off the shower grey water vent and noted the ABS pipe was (factory) sliced off (ripped more like it) below the inner sleeve of the plastic vent cover. Gotcha!, methought. Off came the whole cover, dicor and all. But before extending the pipe and installing a new cap, I thought it prudent to try another water test. A good deal of H2O went down the vent roof opening. Dammit! No leak along the back wall, just ribbons of water twisting around the vent pipe to the floor and out. For some reason-maybe lunch cleared my brain fog-I looked closer at the ragged edge of the vent pipe and noticed a few grains of crud on one side of the pipe lip; like crud that's left at the edge of a mud puddle once the water's evaporated. Another water test, but this time I trickled water only at the crud area. Less than a minute later, water was dripping down the back wall!

OK, here's a forensic guess. First of all the, LL workers goofed by butchering off the vent pipe too close to the roof. With no vent cover sleeve protection, rain splash trickled straight down the outside of the pipe, not just anywhere, but exactly above a location where the vent pipe happened to be wedged against the ceiling opening. From there, the water seemed to have a linear run to the back wall. Maybe, there just happened to be a joint in the ceiling styrofoam at that precise location for the water to follow!

I think it was Malcolm Gladwell who showed how a series of improbable events have downed airliners. Now I can see how that happens! GK

[Merlin]

Good detective work. And thank heavens for aluminum, styrofoam, and azdel. A leak like that could have doomed a wood and fiberglass build.

[Sylvain]

GK I noticed a similar problem on our 13QBB last year.  The ABS pipe was slightly too short inside the cap. 

[GrampaKilt]

Houston, we have a problem! CL owners may want to check the workmanship of their plumbing vents.

The ultimate cause of my water leak was improperly sized roof vent sleeves. Some yahoo used sleeves for 2" ABS pipe instead of 1 1/2". How could anyone be that clueless? After replacing the grey water tank's vent with the proper sleeve, I thought it best to re and re the black tank's. Looking at the dirty styrofoam around the pipe, it was clear that this vent had been letting water into the ceiling for years—I just didn't notice it. The water must have trickled down the rear wall, unseen behind the fridge and upper cabinet and leaving no stain because of the aluminum/styrofoam/adzel construction. CL FTW (at least in that regard)! Add this goof to the list of broken welds, junk valences, cabinet crashes, mis-wired switches and a leaking fresh water tank.

But I still love my CL! GK