Slope
Waste plumbing pipes are often run almost horizontally. Since they depend on gravity for drainage, they must have at least some slope. The slope recommended is typically one-quarter inch per foot. Over time, with house settlement or pipe sag, the minimum slope can be lost. Low spots in waste plumbing may lead to a build-up of waste, effectively reducing the diameter of the pipe, and ultimately result in a blockage. This situation should be watched for and corrected where identified.
Too much slope on horizontal lines can cause siphoning at traps and poor drain performance. Codes specify maximum pipe slopes. The horizontal drain slope should be such that the fall front the trap water level to the vent is not greater than the pipe diameter. A good rule of thumb is five feet as a maximum distance between a trap and a vent.
Leaks
Leakage from a waste plumbing system can, of course, be a health hazard and should be corrected immediately. Leakage may be the result of poor connections, mechanical damage or deterioration of piping. Since the majority of the waste plumbing system in a house cannot be seen, waste pipe plumbing leaks can go undetected for some time, particularly if the amount of water flowing through the pipes is not great. Occasional use fixtures will often have small waste plumbing leaks which are not identified for months or even years.
Corrective action may be patching, or replacement, typically with ABS plastic. Old lead piping is prone to leakage and should be watched closely. It should be replaced if any plumbing work is done on nearby supply piping or fixtures. Similarly, when cast iron waste piping develops several pin hole leaks, or cracks at a seam, it is typically replaced with ABS plastic.
Obstructions
Clogs often develop at traps because the tight corners tend to collect foreign material. Traps should be arranged so that they can be removed easily to clear obstructions. Modem household traps often include a drain plug at the trap bottom. This is useful for removing objects such as rings which are dropped down drains, but may not be large enough to allow clearing of an obstruction. Obstructions are sometimes cleared with plungers or plumbers snakes. In some cases, the piping has to be dismantled. This work can create a health hazard, and great care should be exercised when dealing with any waste water problems. Tools, for example, should be washed after use.
Older homes have traps out in the front yard on the main waste system. These are common spots for obstructions. The waste line outside the house is also vulnerable to tree roots. Where the pipe has not been seriously damaged, a plumbers snake may clear a blockage. If the pipe is broken, digging and replacing are necessary.
Inappropriate Waste Plumbing Materials
Many materials used for waste plumbing were not intended for this use, and may be expected to have a short and troublesome life. These materials include rubber hoses, garden hoses, and non-approved plastic piping. Connections made with the wrong materials or wrong devices cannot be expected to perform properly. Special connectors are provided for special types of piping.
Inappropriate materials raises questions about workmanship throughout the system. Traps and vents are commonly omitted on amateurish installations.
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