Question: I have a home in the Poconos that uses an old-style septic system consisting of a tank and disposal field. The building code now requires a dome system. Where can I get information on building this system and how it works and differs from the ground type?

Answer: Rather than use the phrase "old-style septic system" we prefer to use the phrase "basic" or "conventional." The basic system is alive and well and is still being used in many parts of the country. The dome or mound system that you refer to is a modified basic system and is generally used in areas where the soil percolation rates are poor or where the seasonal water table is close to the ground surface.

Mound systems consist of a septic tank, pumping station and an absorption field that is built into an elevated sand mound. The mound usually consists of at least 12 inches of sand that meets specific guidelines as to clay content and coarse fragments. The sand is covered with gravel, and a 12-inch-deep layer of topsoil is spread over that. The mound must be built correctly or the system will not work properly.

An underground pump chamber is located between the septic tank and the mound. It pumps effluent from the tank to the mound at intervals to prevent the absorption field in the mound from being clogged. The chamber has a capacity large enough to contain one day's sewage flow.

For more information on mound systems write to: Agricultural and Biological Engineering Extension, Pennsylvania State University, 246 Agricultural Engineering Building, University Park, Pa. 16802. Ask for Fact Sheet F-164.

Question: I don't know what it is, but every so often my toilet flushes by itself. It's quite disturbing. About 10 years ago, I had a water pressure reducer put on my water line in the basement. I wonder if this causes it.

Answer: When a toilet flushes by itself in the middle of the night, it's enough to make you think you have a ghost living with you. Actually, there is a simple explanation for the phantom flushing phenomenon.

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The flushing is caused by a deteriorated flapper or tank ball that covers the flush valve opening in the toilet tank. If either the flapper or ball has deteriorated, water will slowly and quietly leak out of the tank. The water level in the tank will drop far enough so that it will trip the fill valve, and the toilet tank will refill with water. This sounds like the toilet has flushed, when actually it is only the tank refilling with water.

When the ball and flapper are badly deteriorated, the leaking water will be quite noisy and noticeable. When they are not badly deteriorated, as in your case, the water loss is hardly noticeable.

To correct the problem, drain the tank and scrub the valve seat with steel wool to ensure a clean, watertight seal. Then install a new ball or flapper.