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But each successive pair must be slightly higher than the pair before. The amount fall drain of this rise must be the same as the amount fall drain of fall the drain is to have. To illustrate: suppose you have decided upon a fall of six inches in every 100 feet. That is equivalent to six tenths of an inch every 10 feet or one and two tenths inches every 20 feet. If your stakes are 10 feet apart, each successive pair must be six tenths of an inch higher than last pair; if 20 feet apart, one-and-two-tenths inches higher. You may establish the correct height of successive pairs of stakes in various ways:with a surveyor's level or a transit if one is available, with a straightedge and level, or with a line level. There are other methods. The important thing is that the measurements be accurate.

Because grades can be very deceiving to the eye you must check carefully the amount fall drain of fall (slope) given the bottoms of the trenches in which the drains are laid. It will not do to merely measure down-ward from the surface because the ground itself is likely to be irregular. Go about it in this way: Stretch a line (string) taut where each drain is to go and fasten its ends to stakes. Next, at the lowest point of the drain (its outlet) drive a stake into the ground on each side of the line and about two feet from it. Let these project about one foot. Make sure that the tops of the two stakes are perfectly level by placing a straightedge from one to the other and checking with a level. At distances of 10 or 20 feet along the line, place similar pairs of stakes, always checking that the tops of each pair are level.

Where they connect with a main drain they should do so at an acute angle in the direction of the flow of the main drain, never at right angles. Side drains should never be brought into a main drain directly opposite each other. Stagger them so that the flow of water from one lateral doesn't interfere with that of another. Avoid, whenever possible, running drains where the roots of trees are likely to get into and clog them.