Raw sewage is mostly water.
The sewage flows down the drain pipes into a septic tank. The tank is pretty large and is buried between the house and the forest. There is a concrete deck on the top.
In the septic tank, the solids in the sewage naturally settle to the bottom, this is the sludge. The dirty water, called effluent, floats at the top. The effluent, which is actually full of nutrients, is drained off into a “leaching field” in the forest and absorbed by the earth.
Most septic tanks have pumps to suck the effluent into the leaching field. Ours does not - it is gravity fed. This is unusual and confuses most plumbers, who expect a pump breaker and alarm inside the house.
The sludge needs to be pumped out of the septic tank and hauled away every 4-5 years. Flood in Millerton usually does this. If it's not done, the sludge starts backing up into the house. It will appear in the basement shower first, and you'll know it.
Some other blockage can cause a backup as well; a plumber needs to be called.
A dehumidifier does an excellent job of keeping the putrid smell to a minimum. Ask me how I know.