To the Editor: We install risers on 95 percent of the tanks that we dig out, especially on concrete tanks. The following isn’t an issue for plastic or fiberglass tanks.We explain to our customers the deterioration process that happens to the concrete, in the air space above the water level, when the corrosive gases are trapped in the tank. We suggest wedging the tank lids open about 1/2 inch and drilling a few holes in the top of the riser lids. This allows the expansive gases moving up through the house’s sewer gas vents to pull air through the tank
