|Posted by ED on March 26, 2004 at 20:52:12:|
|In response to Re: question on running a vent|
AN S trap is an old style of trap. Used in old plumbing systems where the drain normally came out of the floor rather than the wall. These are NOW illegal in most jurisdictions because of what Deb said...they siphon the water very easily and permit sewer gases to emit from the drain where the trap has been siphoned.
What she mentions is that tying into the system as you describe would create a similar situation to an "S" type trap.
Every fixture needs a vent in order to drain properly and to prevent sewer gases from entering the system. There are numerous ways to vent a fixture, but there definitely are RIGHT and WRONG ways.
Plumbing IS a science! There has been about a hundred years to perfect the science. In old days before modern venting, like around the turn of last century, people used to place their toilets outside (not outhouses) in a separate room, because of the noxious sewer gases, that they could not figure out how to alleviate. Around the 19 teens to 1920s this was finally figured out.
It's not rocket science but it still is very important to follow the generally accepted practices of venting.
I hope this helped answer your concerns.
: : We plan to tap into this exisitng inch and a half galvanized drain-well we want to replace w/ pvc and join the new sink dain into the tub drain.
: : My question is I do not see a vent for this tub drain- my guess is that it is vented underneath somewhere?? If it is indeed vented somewhere can I just tie in the new sink drain and not have to run a separate vent b/c there is one for the tub already and the new sink drain will be part of the existing tub drain?
: : your help and opinion is greatly appreciated,
: : regards,
: Generally speaking, you cannot connect a drain in the section of pipe that runs from a fixture p-trap to its vent (this section of pipe is called a trap arm). On a sink there is no way to connect without venting the sink. Any attempt to connect to the tub drain will create an s trap. S-traps will siphon dry and allow sewer gas to enter the house. The sink will need a vent that rises straight up at the sanitary tee that is the drain/vent/trap arm junction. It can 90 or join with other vents 6" above the flood rim level of the fixture. If this is not a bathroom sink (a lav), but a kitchen sink, you need to use 2" drainage pipe.
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