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RepWars Briefing - Questions & Answers
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Question...
"This question concerns using sanitary tees for venting. When venting a horizontal waste pipe can you use a sanitary tee, in-line with waste pipe, with branch inlet in vertical or offset no more than 45 degrees from vertical? "

RepWars Reply...
A sanitary tee installed horizontally is not considered a drainage fitting. Remember, any fitting located lower than six inches below the overflow of a fixture must be a drainage fitting (even if it is being used as a vent). The reason for this is to allow any waste that may back up into the vent piping the ability to drain back down into the drainage system. The proper fittings to use for the arrangement you mention is a combination wye and eighth bend.
Some local authorities do allow the use of horizontal sanitary tees below the flood rim level (as an exception). For example, the State of Oregon amends the Uniform Plumbing Code to allow this. You should check with your local code authorities if you really need to use a sanitary tee in this arrangement. Sometimes, in situations where space is limited, it is impractical to use a wye and eighth bend. If this is the case, your local inspectors may allow a sanitary tee.



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