Small pipes are lowered into the trench and swung into position on a hook as shown in Fig. 124. Pipes up to 15 or 18 inches in diameter can be handled by the pipe layer and helper in the trench without assistance. Heavier pipes may be lowered into the trench by passing ropes around each end of the pipe. One end of the rope is fastened at the surface and the ropes are paid out by the men at the surface as the pipe is lowered. If the pipes have been fitted together and marked at the surface it is undesirable to use this method of lowering as the position in which the pipes arrive in the bottom of the trench can not be easily predicted. A cradle may be used for shoving the pipe into position as is shown in Fig. 125. [Illustration: FIG. 124.—Hook for Lowering and Placing Sewer Pipe. ] [Illustration: FIG. 125.—Cradle for Placing Sewer Pipe. ] Pipes above 24 to 27 inches in diameter are too large to be handled from the side of the trench. A hook as shown in Fig. 124 is placed in the pipe so that it will be in the proper position when lowered. It is raised by a rope passing through a block at the peak of a stiff-legged derrick which spans the trench, or by a crane. If a derrick is used the rope passes to a windlass on the opposite side of the trench from the pipe. Mechanical power may be used for raising pipes too heavy to be raised by hand. The pipe is then lowered and swung into position while supported from the derrick. Excessive swinging is prevented by holding back on the guide rope as the pipe is raised and lowered. Pipes are usually laid with the bell end up grade as it is easier to fit the succeeding pipe into the bell so laid and to make the joint, particularly on steep grades. The Baltimore specifications state: The ends of the pipe shall abut against each other in such a manner that there shall be no shoulder or unevenness of any kind along the inside of the bottom half of the sewer or drain. Special care should be taken that the pipe are well bedded on a solid foundation.... The trenches where pipe laying is in progress shall be kept dry, and no pipe shall be laid in water or upon a wet bed unless especially allowed in writing by the Engineer. As the pipe are laid throughout the work they must be thoroughly cleaned and protected from dirt and water, no water being allowed to flow in them in any case during the construction except such as may be permitted in writing by the Engineer. No length of pipe shall be laid until the preceding length has been thoroughly embedded and secured in place, so as to prevent any movement or disturbance of the finished joint. The mouth of the pipe shall be provided with a board or stopper, carefully fitted to the pipe, to prevent all earth and any other substances from washing in.