Q: I have recently acquired a used mahogany baby grand piano. It has no nicks, severe scratches or stains. But there seems to be layers of white furniture polish combined with lots of dirt that have dulled and dirtied the finish. How can I remove the old wax and dirt and restore an attractive shine?

A: As a rule, the most effective way is to use a solvent such as paint thinner (which is flammable, so work in a well-ventilated room with no open flames near by). Dip a sponge into the thinner or solvent, scrub a small area at a time, then immediately wipe off with a clean rag. After one side or the top is done, use clean thinner and a clean rag and wipe off again with a dry rag. The surface should now be clean, free of wax, and ready for polishing. I recommend an oil-type polish for your piano rather than a conventional wax.

Q: The wash basin in one of the bathrooms in my house drains very slowly. My husband says the slowness is due to an air lock and nothing can be done about it. Do you have any suggestions?

A: First, see if you have a partially clogged drain. If the drains are clear (in the wall as well as under the sink), it may be that the vent pipe that goes up through the roof is clogged. This would cause what your husband refers to as an air lock. It can be corrected by clearing the pipe. A plumbing contractor should be able to take care of this for you.

Q: With the arrival of cold weather I turned off the inside water valve in the line that supplies water to my outside garden hose connections. Now my question is: Should the faucet on the outside be left open or closed during the winter?

A: The faucet should definitely be left open. That way any water still in the pipe between the inside valve and the outside faucet, or in the body of the outside faucet, will escape safely. Even more important, should the valve on the inside leak slightly during the winter (not uncommon for these valves), water would not accumulate inside the pipe -- it would run harmlessly out of the open faucet on the outside.

Q: I recently purchased an 18-year-old house and I find that the varnish used on the kitchen cabinets has changed in color and appearance -- apparently because of the heat from the stove and the oven. How can I clean or restore the varnish on these cabinets to its original appearance?

A: It depends on whether this is merely a surface discoloration or if the varnish has actually changed color. You don't say how far from the stove and oven the cabinets are, but generally, if heat affects the finish it is only directly over or next to the stove -- not in the entire kitchen. Try cleaning with a commercial furniture cleaner or solvent, or sponge lightly with detergent suds. If the finish looks cleaner and lightens, then you know it is surface soil and can be removed. If heat has actually darkened the finish, then the only cure is refinishing.

Q: We live in a ranch-type house that we moved into in the spring of 1977. That fall we noticed that after a freezing night the edge of the ceiling got wet as the temperature rose above 32 degrees, even if it did not rain before the freeze. One roofer said condensation was the problem and he made some openings around the eaves and more near the top of the roof. He also put a lot of insulation into the attic. None of this seemed to help. I might add that the house itself tends to be damp and all the windows sweat a lot. Do you have any suggestions?

A: I agree with the roofer who felt that your problem was condensation. Ice is probably forming on the attic beams and as it melts it runs down and shows up along the edges of the ceiling. There are several possibilities: It may be that the insulation installed in the attic is blocking the vents or openings along the eaves; it may be that there are not enough vents (not large enough, not enough of them) to properly ventilate the attic above the insulation; or it may be that the insulation on the attic floor does not have a proper vapor barrier, so warm moist air from below is finding its way into the attic and forming condensation on the cold surfaces. The fact that all the windows downstairs sweat a lot indicates that the overall humidity inside the house is too high.