Channels should be laid down the centre of each stall and along the passage behind. The channel may be semicircular, of cast-iron, with a perforated flat top, in sections made to slide, so that by removing one of them the attendant can slide the other pieces along and clean out the whole of the channel (fig. 471). By discharging the waste water from the drinking-pot into it the flushing of the channel is rendered easy. Some persons prefer an entirely open gutter (fig. 470), as being less liable to choke up from neglect. The chief objection to open gutters is that they allow the liquids to be absorbed by the bedding, retaining them within the stable and vitiating the air. Musgrave's pattern, as shown in fig. 577, has a fall in itself, and is often used; the channels or corrugations provide for the flow of liquids to the drain, while the surface is almost level, and offers a good foothold for the horse.
Fig. 576. - Musgrave's Horse-tying Arrangement.
The underground drains should be made of glazed stoneware or cast-iron pipes, laid upon concrete and jointed in the best modern manner. It used to be the idea that, on account of the great percentage of solid matter contained in the drainage from a stable compared with the liquid portion, a very large diameter of pipe was necessary. The theory of large pipes for house-drainage is now quite exploded, and there is no reason why it should be retained in the case of a stable. The contrary rather should be the case, for a small pipe running nearly full will be better flushed, and there will be less deposit of sediment than with a larger one.
The same arrangements must be adopted for stable drains as for house drains. All inlets to the drains ought to be outside the building, as shown in fig. 574, and ought to be trapped. The trap shown in fig. 475 can be used for this purpose. The surface drainage from the stable ought to be carried through the wall by an iron pipe discharging over the basket in the trap, and to prevent to some extent the risk of foul air being drawn through the pipe into the stable, a hinged brass flap (fig. 473) may with advantage be fitted on the outer end of the pipe. It is desirable to have an inspection-manhole with an air-tight cover at every change of direction or important junction, so as to obviate as far as possible any necessity for lifting the drains and breaking up the yards and pavement. Another manhole must be constructed at a short distance from the point at which the drain is connected to the public sewer or to the private cesspool or underground tank, and in this manhole an intercepting trap must be placed to prevent foul air from the sewer or cess-pool from entering the drains. To ventilate the drains an opening for air must be formed in this manhole, and at the head of the drains a drawn lead or cast-iron ventilating: pipe not less than 3½ inches in diameter must be carried up the building outside. These are shown in fig. 476.
Fig. 577. - Musgrave's Patent Open Surface-gutter.
The chief features of a stable trap are that it should be very strong, and afford a good foothold for horses, and that the attendant should be able to get his hand into every part. If by any accident it should be left open, the horse should not be likely to be injured if he put his foot into it; the trap should also provide as easy a flow for liquids as is compatible with a sufficient water-seal. Winser's stable trap, shown in figs. 474, 475, p. 85 of this volume, fulfils these conditions, and contains a perforated metal basket which prevents straw and dung from entering the drains.
Some corporations do not allow any connection between stable-drains and the public sewers, and an intercepting tank may sometimes be required. This tank should not be too large; it should be impervious both at the sides and bottom; the top should be closed with air-tight cast-iron cover, and due means should be taken for ventilation. Such a tank, however, must be viewed with more or less suspicion, and perhaps the safest way is to place it in a spot as little frequented as possible, with a ventilating grid made to lift easily, and to have it cleaned out at very short intervals.