It is frequent now, and a very good practice, to make an air opening at about the level of the ground, leading into the drain just on the house side of the trap which separates the drain or house sewer from the main sewer, and this is a very good plan provided the opening is not too near to a window, as where it is adopted foul air cannot accumulate in the drain.

I have already spoken about the waste-pipe of the cistern, and that ought always to end outside the house in the open air. The other pipes that ought to end in the same way outside the house, and that very seldom do, are the waste-pipes from the sinks, from the bath, and all waste-pipes of that kind; they all, as a rule, go into the drain. You will say, if you allow these pipes to end over the yard, the yard gets into a great mess, but then that is better than to have half a dozen pipes going into the drain, and allowing foul air to get into the house through them. You can, however, avoid that in several ways. There must be some kind of trap to carry away the rain water. Now, sometimes the syphon trap is used, a trap with an open gully, and then a syphon-pipe leading from it, so that it holds water up to a certain level, and a very excellent kind of trap it is. If you want to make a sink-pipe or bath-pipe end away from the drain, you need not have the end over the surface of the yard, but you can have one of these syphon-traps with a hole in the side which is above the level of the water in the gully, so that the wastepipe-comes in under the grating, but above the water in the trap, and is thus completely disconnected from the drain.

In order to prevent foul-smelling air coming up sink waste-pipes, it is well to have a trap of some kind below the sink, not for the sake of keeping out drain air, but for the sake of preventing a draught from coming in tainted with foul matter from the waste-pipe itself. There ought, then, to be a syphon-trap immediately below the sink, and it is a good plan to have one with an opening closed by a screw cap for the purpose of clearing the trap in case it should get stopped up. Sometimes what is called a D trap, from its shape, is used for this purpose. The pipe ought to be carried through the wall and made to end in the side of a syphon-trap underneath the grating, but above the level of the water in the trap, so that practically the pipe is cut off from the drain. For downstairs sinks there is a trap which does admirably well, and requires no trap to be placed upon the sink-pipe; it is called the Mansergh-trap. The sink-pipe goes ' in through an aperture in the side of it into one compartment, and is turned downwards, so that the sink-pipe is trapped itself in the water contained in the first compartment ; then the water flows from the first compartment through an aperture into the second compartment, and over these two compartments there is a loose iron lid with openings in it, and then from the second compartment the water flows under a partition into a third, which is closed, and from the third compartment it flows through an outlet into the drain, and there is another outlet in the third compartment to which a ventilating-pipe may be attached.

I warn you against having openings of any kind into the drains from the basement It is a very common thing to have a trap under the tap for the kitchen boiler, leading into the drain; these are most dangerous things to have. If the sinks, baths, and waste-pipes are cut off it is perfect folly to have traps in the floor of the house connected with the drain, and the greatest danger of all is to have a trap of the kind commonly known as the bell-trap, in the floor of the house connected with the drain; it is one of the worst contrivances ever devised, and has no redeeming point. It consists of an iron box through the bottom of which a pipe passes to the drain; the cover is a perforated plate which has a bell-shaped piece of metal fixed into its under surface ; when the cover is in place the bell is immediately over the top of the pipe which projects above the bottom of the box, and the rim of the bell dips into the water, which of course stands in the box at the level of the mouth of the pipe. The disadvantages it has are: that the water is only about half an inch deep, so that the pressure of the air in the drain is often sufficient to drive the foul air through that small quantity of water; the difference between the temperature of the air in the kitchen and that in the drain is sufficient to cause this foul up-draught, especially when some of the water has evaporated; and that whenever the top is removed the trap is gone, and these traps do not let the water run very readily, consequently the trap is frequently taken up, and the foul air gets, into the house, causing diarrhoea, typhoid fever, and so on.

Water-closets should be of as simple a construction as possible ; hopper closets with flushing rims and 1£-inch supply-pipes are well suited for general use. Pan closets are bad contrivances, on account of the large iron " container" which always becomes foul; valve closets are far better. D traps should never be used, but always S or P traps, and when a leaden tray or "safe" is placed under a water-closet or a bath, the waste-pipe from it must go through the wall into the open air, and not be joined to the closet trap.

With regard to sanitary matters connected with towns, all sewers of towns ought to be well ventilated at the level of the streets, else foul air will come from them into the houses. The common sewers of towns ought always to end freely; if they end under the level of the sea or of a river, the water will be backed up in them some time or another, and foul air will be produced in the sewers and spread disease in the town. The only instances in which adoption of the water-carriage system in towns has been attended with an increase in the death-rate from typhoid fever have been instances in which the common sewer has ended under water. In all other instances, without exception, where the water-carriage system has been introduced, the death-rate from this fever has been diminished, and cholera abolished. What is to be done with the sewage from the towns ? It is commonly turned into rivers. The Eomans found out how convenient the drains were to convey refuse matter away from the towns, and the natural place to end the drains was the river, and that is why our sewers now in the great majority of cases end in the rivers. The evils of this are that the sewage makes the rivers foul, renders the water unfit to drink, and, in the case of small rivers at any rate, the sediment blocks up their course.