The minimum size adopted was 24.3 cm. (8 in.) in internal diameter. The sewers of diameters between 24.3 and 50 cm., are 0.91 m. (36 in.) long, and are of salt-glazed vitrified clay, imported from San Antonio, Tex.
Table 12 gives the details of the length of the various sewers laid.
TABLE 12.—Length of Sewers.
| Diameter: | Kind. | Length, in meters. | |
| cm | in. | ||
| 24.3 | 8 | Fire clay | 38,332.85 |
| 25.4 | 10 | " | 16,400.69 |
| 30.5 | 12 | " | 7,953.15 |
| 38.1 | 15 | " | 4,850.56 |
| 45.7 | 18 | " | 2,023.40 |
| 50.8 | 20 | " | 1,450.53 |
| 55.9 | 22 | Reinforced concrete tubes, 6.9 cm. thick | 3,134.20 |
| 61.0 | 25 | Reinforced concrete tubes, 7.6 cm. thick | 357.40 |
| 68.6 | 27 | Brick and concrete | 484.05 |
| 76.2 | 30 | Brick and concrete | 662.69 |
| ——— | |||
| Total | 75,649.15 | ||
The greater number of the manholes are of brickwork, 23 cm. thick, and have concrete inverts. They have a diameter of 1.2 m., which is reduced to 0.61 m. at the top, and each is provided with a heavy cast-iron frame and closed cover weighing about 190 kg. There are 521 manholes, and they are placed at every block and on long lines about 80 m. apart.
Fig. 16.—Standard 300-gal. Flush Tanks.
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The sewers are flushed with 15-cm. (6-in.) automatic flushing siphons of the Miller pattern with 20-cm. (8-in.) discharge pipes. There are 278 of these siphons, and they are placed in flush-tanks (Fig. 16) built of brickwork and plastered with 1:1 cement mortar. Their capacity varies from 800 to 1,200 liters, and they discharge from 221⁄2 to 281⁄2 liters per sec. They are timed to flush once in 24 hours.
The system is at present ventilated by 23-cm. (9-in.) steel ventilating columns (Fig. 16), with ornamental cast-iron bases. There are 220 of these columns. Most of them are 7.85 m. above the level of the edge of the sidewalk, and are connected to special 15-cm. branch pipes leading from the sewer on the outside of the flush-tanks. In the center of the city they are provided with extension lengths, giving a total height of 12 m.