This section is from the book "Cassell's Cyclopaedia Of Mechanics", by Paul N. Hasluck. Also available from Amazon: Cassell's Cyclopaedia Of Mechanics.
To tell whether a drain is properly or improperly laid, exposing it only at two points, the following tests maybe employed, (a) Put a measured quantity of water in at the top end and see if the same quantity escapes at the lower end. (b) Allow water to flow through, and then look through the drain and note if all the water has passed away or whether some is retained in bagged parts. At the same time note if the drain is " like a gun-barrel" or crooked, (c) Float apples, small potatoes, or something similar, through the drains to test if there are any obstructions that would arrest floating matters, (d) Float a cork with attached cord through the drains, and by such aid drag a drain-bobbin through, (e) For fall, place levelling staffs on the inverts at each end and use a sighting level on the surface, or a straightedge and pocket level can be used; or if) bends and upright pipes can be temporarily connected to the ends, the whole filled with water, and the depth at each end measured. This would also test the soundness of the drain.