(2.) The internal diameter of the drain should not be too large; 6 inches may be considered as a maximum, 4 inches is generally quite sufficient to carry off all the sewage from an extensive establishment, even if all the water from the roofs or a portion of them is included. (3.) The inclination is governed by circumstances, but about 1 in 60 is found to be a very convenient fall for many hydraulic, and other reasons. (4.) The jointing of the pipes should be executed with great care; if cement joints are made each pipe should be jointed separately, and it should be seen that no cement is left in the drain. Sometimes tarred gaskin is used to prevent this, and Stanford’s patent joints are excellent where running water or sewage has to be contended with, or great despatch of the work is necessary.[214] (5.) The sockets of the pipes should be sunk into the ground at the bottom of the trench so as to give an even bearing, which amongst other benefits dispenses with the chance of settlements. (6.) No pipes should be allowed to be covered in until they have been inspected by the town surveyor or his assistants, and in order to test the soundness of the joints, it is a good plan to fill the drain with water, having first stopped up the lower end, and note the effect. (7.) Drains should not pass under buildings if it can be avoided, but if unavoidable they must be buried in good concrete, and relieving arches turned to any walls passing over them. In America iron pipes are used under houses. (8.) Care must be exercised, in filling in over pipes, not to break or injure them. (9.) The trap to a house drain should be a “Buchan” or other similar syphon with a good cascade action, its position must be guided by circumstances. (10.) The drain should end at the outside wall of the house and be carried up the wall its full diameter to above the roof for ventilation, an inlet for fresh air being essential on the house side of the trap; if the drain has to pass under the house it must be similarly carried up on the other side. (11.) The connection with the main sewer has been already described. In conclusion I would urge the necessity of a register of all drains being kept that are examined by the surveyor’s department. This can be done by having a series of numbered notebooks kept solely for this purpose, and all the information thus acquired should also be plotted on the map of the town if on a sufficiently large scale. The necessity of correct plans of the drainage of buildings cannot be over-estimated, especially for hospitals, asylums, workhouses, schools, or other public buildings, and even for the smallest dwelling house such a plan would often prove to be the greatest boon to the occupier or owner as well as at all times to the town surveyor, the medical officer of health, and the inspector of nuisances. [207] For definitions of the word “sewer,” see the chapter on Sewerage.