A: No, not by itself. The key is vent distance and trap-arm rules, not the total drop to the main.<\/strong><\/p>\n One vent can protect more than one fixture.<\/p>\n In many designs, the lavatory is the dry vent.<\/p>\n The lav drain also acts as a wet vent.<\/p>\n That wet vent can serve the toilet and shower.<\/p>\n This is often called a \u201cbathroom group\u201d wet vent.<\/p>\n You do not need to dig 4 feet everywhere.<\/p>\n You only need full depth where you tie into the main.<\/p>\n The goal is a clean, sloped branch drain.<\/p>\n Then you \u201cdrop\u201d once, near the main connection.<\/p>\n The shower and sink have separate traps.<\/p>\n After the trap, keep the trap arm mostly horizontal.<\/p>\n Vent the trap arm before any big vertical drop.<\/p>\n A vertical drop before venting can siphon the trap.<\/p>\n That can lead to sewer gas smells.<\/p>\n This is a common \u201cone-bath group\u201d approach.<\/p>\n Use long sweeps where the flow turns.<\/p>\n Plan a cleanout where you can reach it.<\/p>\n Future you will be glad.<\/p>\n It sounds simple, but it is risky.<\/p>\n The shower and sink still need vent protection.<\/p>\n They cannot just drop 4 feet unvented.<\/p>\n You can drop after the vented section.<\/p>\n But vent first, then drop.<\/p>\n Codes vary by area.<\/p>\n If this is permitted work, ask your inspector early.<\/p>\n Bring a simple sketch with pipe sizes and distances.<\/p>\n I’m Chris Mayer, writing for Plumbing 101<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"What \u201chorizontal wet venting\u201d means<\/h2>\n
![\"Deep](\"https:\/\/plumbing101.i234.me\/wordpress\/wp-content\/uploads\/2025\/12\/Deep-Main-Drain-Wet-Vent-This-3-Fixture-Bath-300x200.png\")
The rules that usually drive the layout<\/h2>\n
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Why are the big main changes in your plan<\/h2>\n
Do not create an S-trap on the shower or sink<\/h2>\n
A layout that often passes inspection<\/h2>\n
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What about \u201cthree vertical drops\u201d to the main?<\/h2>\n
Key measurements to confirm<\/h2>\n
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Helpful external resources<\/h2>\n
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