Welding cracked plastic septic tanks: a repair without a watertightness test is just a plaster

You offer repairs of plastic tanks buried next to houses: wastewater holding tanks, septic tanks, home treatment plants, rainwater tanks and manholes. The typical job is a crack in a wall or the base that would otherwise mean replacing the whole tank with an excavator. You weld with an extruder and filler rod of the same material, polyethylene or polypropylene, because each only welds to itself. Then a watertightness test confirms the tank holds again and you issue a report. With a wastewater holding tank the law adds pressure too: in many countries it must be watertight and leakage can be fined. The catch is twofold. A crack almost always has a cause, most often groundwater buoyancy after emptying or missing concrete anchoring, and if you don’t remove it, the tank cracks again. And you must never enter a tank without ventilation and gas measurement: hydrogen sulphide dulls the sense of smell and can knock a person unconscious in moments.