Do not pour hot water or antifreeze down the line and do not run a flame near it. Add insulating cover over the line and tank, keep normal warm water flowing, and call for a professional thaw. Most freezes are in the line, not the tank.
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Freezing is nearly always a line problem rather than a tank problem. An active tank generates its own heat from biological activity and holds a large thermal mass, so it rarely freezes solid. The vulnerable points are the run between the house and the tank, the outlet line to the field, and any shallow or exposed section. The conditions that cause it are consistent: a hard freeze with little snow cover, since snow is the insulation that normally protects the run, plus low water use. A vacant house, a household away for the holidays, or a seasonal property is the classic setup, because a line only stays clear if warm water moves through it regularly. What helps immediately. Keep using warm water at a normal cadence rather than stopping, since flow is what keeps the line open. Add insulating cover over the tank and the line run: straw, leaves, or a tarp weighted down all work, and undisturbed snow is better than a cleared path. What to avoid. Antifreeze of any kind, which kills the bacterial population and is a groundwater contaminant. Open flame or a torch near a plastic line, which melts it. Boiling water poured down a frozen line, which usually refreezes further along and moves the blockage rather than clearing it. A professional thaw uses steam or a jetter and clears the ice without damaging the pipe. On pumping in winter: it is possible, and access is the constraint rather than the tank. Frozen ground over a buried lid means excavation in frozen soil, which is why a riser installed at grade is worth having before winter rather than after. the mix of pre-war stock in the older Columbus neighborhoods, mid-century ranches in the inner suburbs, and large 1990s-onward subdivisions in the outer counties