Septic and drains after the flood.

Not while the ground is still saturated. An empty tank in waterlogged soil can float upward and damage the inlet and outlet pipes, which is a far larger repair than the pump-out would have been. EPA guidance is explicit about this, and New Mexico Environment Department material notes plastic and fibreglass tanks are the most likely to lift. Wait until the water table has dropped below the drain field, then have the tank pumped — at that point it does real good, because it clears the silt and debris the flood pushed in.

After a flood it is usually the ground rather than the tank. A drain field works by letting liquid soak away into the soil, and soil that is already full of flood water cannot take any more, so everything upstream slows down. The giveaway is timing: if it started when the water came up and the field area is wet or standing, the system is backed up because it has nowhere to drain, not because the tank filled unusually fast. Cutting water use hard and waiting for the ground to drain is what helps.

It depends on how saturated the ground got, the soil type and how fast the water table drops, so no one can give you an honest number for your property on day one. The practical test is the one EPA describes: the system should not be used until the water in the soil around the drain field is lower than the water level around the house. Until then, every flush is going somewhere it cannot be treated. Reducing water use is what shortens the wait.

Pumping standing water off the surface does not drain the soil underneath, which is where the problem is, and the traffic involved usually does more harm than good by compacting wet ground. The field recovers as the water table falls. Keep vehicles and equipment off it, keep water use down, and let it drain.

Treat it as contaminated. Bloomfield reported that flooding forced a temporary shutdown of its water reclamation facility, which allowed raw sewage into the river and the surrounding floodwater, and any yard with a flooded septic system has its own contamination to consider. Boots and gloves, keep children and pets out of standing water, wash thoroughly afterwards, and clean anything indoors with detergent and then a bleach solution.

If you are on a private well, have the water tested for bacteria before drinking it again, even if the wellhead never went under. New Mexico guidance is clear on that, and the New Mexico Environment Department Drinking Water Bureau can point you to certified laboratories. Use bottled water in the meantime. Wells that were submerged usually need disinfecting as well, and that is work for a well or pump contractor rather than a homeowner.

Looking in is not worth it. The gases inside a septic tank can be fatal very quickly, and that is true whether or not there has been a flood. Check from the surface that the lid is seated and secure, and leave opening it to someone equipped for it. There is nothing visible from the top of an open tank that changes what you should do next anyway.

Leave it off until the connections have been looked at. EPA guidance is to examine all electrical connections for damage before restoring power, and submerged pumps and control panels are exactly the components to be careful with. Switch it off at the breaker and have it checked rather than finding out by energising it.

Silt and debris, as much as sewage. Flood water carries fine sediment into tanks, pump chambers and lift stations, and if that silt is left it moves on into the drain field and clogs it, which is the expensive failure. A pump-out once the ground has drained clears that material out while it is still in the tank. It is also the one opportunity to see the condition of the baffles and the inlet and outlet.

That is common, and it is worth finding before anything else needs doing rather than during an emergency. Property records and the original permit often show the location, and the New Mexico Environment Department holds septic permit records. Failing that the line leaving the house gives the direction, and a locating tool traces it to the tank, which is quicker and far less destructive than digging to find out.