Black Water Tank Repair

When the bathroom floor rotted away, the 16 gallon black water tank, which sits directly beneath the toilet, was left holding the weight of a 50+ pound ceramic Aqua Magic Deluxe toilet. Probably exacerbated by the drive home from the previous owner’s house, the black tank cracked around the toilet flange. But since the cracks were confined to the top of the tank, I decided the damage could be successfully repaired.

First, all the cracks were stop-drilled to prevent further cracking. Then each crack was superglued and duct-taped simply to hold the cracked area in alignment during the course of the repair. Since the top of the tank had bowed downward due to the toilet sitting directly on it for so long, elevator bolts were hot-glued to the most depressed areas, and fitted with strips of hardwood supported on tank’s perimeter.

Supporting the odd shaped tank on its original Styrofoam bed, an old (i.e. low heat hi airflow) hair dryer was used to heat the interior of the tank. At suitable points in the process, all the bracing’s hardware was tightened up to hold the top in its new position. Of note, this process took place over the course of a day or so as I did not want to either melt the tank, or make any new cracks by proceeding too fast.

Research indicated a high probability that the tank was made of ABS plastic. Confirming through a simple test that ABS Cement did indeed chemically melt the surface (solvent weld), I contacted a local plastics vendor who sold me a small sheet of ABS plastic approximately the same thickness at the tank’s top, and just large enough to cover the cracked area. Black in color, you can see it in the lower RH image.

After removing all duct tape, and coating both the new plastic scab & the top of the tank with ABS Cement, the scab was set in position, supported and allowed to dry for several days.

Subsequent inspection of the interior showed that the ABS cement had actually squeezed through the stop-drill holes, and that the superglue hung on long enough to keep the cracks together before the solvent weld completed its job. I think the repair will stand the test of time & rough roads!