If you wish to know what size to make such a tank, ascertain how many square yards of ground your roofs cover. About one hundred and twenty-six gallons of rain-water fall on an average every year upon a square yard of ground: a cubic foot of water is equal to about 65 gallons; you can therefore easily judge what size to make your tank.

Touching upon soil pipes and cesspools in private houses where there are no public drains, I would say that too much care cannot be taken to provide for circulation of air in all pipes leading to and from cesspools. Connect these pipes with a 4-inch tube and carry it up higher than your chimneys on some stout lofty tree, or on some building at a short distance from the house, if possible, and towards the south of the house - as such air generally works towards the sun and away from the house, if let out south of it.

For your water-closets you will find a good D trap about the best check to any pressure of sewer-gas, as it will not be forced through a D trap so easily as through some of the modern shallow traps and syphons; but if you happen to have valve-closets, or light traps, a lead pipe can in most cases be put into the leaden bend and carried above the roof; then you will have an effectual safeguard. E. g., it will be evident to all that when water goes down a soil-pipe a certain quantity of air must be displaced; this air will rush out into the closet unless ample provision is made for its escape elsewhere; and as the act of a person pulling up a closet-handle is first, to stoop, which causes him to emit his breath, and then to raise himself, which causes him to inspire, it will be readily noticed that he is sure to take in his breath at the moment when the water runs down the soil-pipe and the pent-up sewer-gas rushes out close to his lungs. Keep the closet seat-flap down, cut holes in the flap to admit of the handle being raised when the flap is closed; it will, however, be far better to ventilate your soil-pipes and drains. Water-closets should be flushed with a large pail-full of water now and then, because the small quantity of water coming in through the supply-pipe into the pan is insufficient for this purpose, especially when the handle is held up a very short time. Jenning's and Underhay's pans are better supplied with water than many, but even with these arrangements no sufficient flush takes place to well push on the excreta. When these accumulate, poisonous matters are formed and danger springs up, but there is not the same danger from fresh sewage. Do not allow slops to be emptied down your water-closets, because some may be spilt and get between the seat and the pan, and gradually saturate the woodwork beneath, causing decay and unwholesome faint smells. Have a pad of dry hair-felt, sewn in an oilskin cover, placed between the top of the pan and the wooden seat, if there is any vacant space there; this will stop draught and the splash referred to.

Lime-white with hot lime the floor and inside of the seat-enclosure annually; this can be readily done by taking off the top or seat.

The effectual ventilation of water-closets, situated as they often are, is by no means an easy matter. If you open the window, the warm house will quickly receive the smell you intended to go outside, and you will soon perceive that the air will not obey your commands. Have a space (however small) between the inner and outer doors of the water-closet; if this space is too confined for a window, get external air into it by tubes; this stratum of air will materially assist you, because it tends to balance and check the progress of the air in the water-closet beyond; but the better method is to lead a tube from the ceiling of the water-closet into the nearest chimney-flue where there is smoke ascending, or where there is sufficient warmth to make it act as you wish; your water-closet will then soon be cleared of all disagreeables. A valve, however, should be balanced in this tube to prevent any sudden down draught.

Some provision should be made for disposing of slops entirely away from the water-closet. People are little aware what odd things are put down water-closets. If plumbers told people the queer things they find in water-closet pipes, they would not be believed. Water-closets should be strictly guarded, and domestic servants cautioned against misusing them. The same oversight should be given to traps in sinks and elsewhere; these traps are often lifted off and not put on again, resulting in much damage to the health of the servants and all the inmates of the house. Let all pipes from sinks, butlers pantries, baths, etc., discharge themselves free to the air before entering sewer drains: this plan can generally be carried out without difficulty or unsightliness.

Have all junctions of water-closet pipes with the drains examined now and then, as the stopping often shrinks and the lead decays, especially if the stopping is made of Portland cement. The seating or fixing of the pan on to the soil-pipe should also be examined periodically, so as to stop any leakage of sewer-gas.

All cisterns should be cleaned out once a year, and any deposit removed. If you have a "waste-pipe" in your cistern branched into the soil-pipe, which is too frequently the case, look well to it, for unless your drains are sufficiently ventilated, the sewer-gas will be forced through the waste-pipe and may be absorbed by the water in your cistern. If you have a painted lid to your cistern, see if any discoloration has taken place; if you find such to be the case, you may be sure that sewer-gas has escaped into your cistern.

If you have drains from your basements and cellars, be particularly careful to see that the traps are efficient and kept well supplied with water; the great importance of having this seen to is self-evident. Where do you suppose the supply of air to your sitting-rooms is frequently drawn from? If they happen to be over rooms or cellars with plastered ceilings, air will percolate from these into your sitting-rooms. You can prove this by blowing a cloud of tobacco-smoke below; or you may find it out accidentally through something being spilt, such as paraffin oil for instance. Have your cellars frequently lime-whited and the floors cleaned.