Each sink,toilet tub etc. should be trapped. this prevents any smell from comming up into any of the before mention. Double trapping is not a good idea because it ma cause a vacuume between the 2 traps....Understand?

good luck

Thanks Hollywood. Now an even more obvious question...does each fixture (toilet, lav, shower, tub) need to have its own vent? The current configuration consists of a bunch of drains running into the main stack, which is vented. Is that insufficient, and should it be addressed asap....or is it something that isn't super important?

sorry it took so long to reply... Only 1 vent necessary. Should be in the main,...running to the sewer. Sounds like it's OK......and NO, Only the mains need a vent. The Idea of the vent is to break any vacuume that may occure if,..say all the drains are draining water. The main vent is usually at the upper most point of the main. This releives any vacuume situations when the many gals. of water are rushing to that common end point.......

[This message has been edited by HOLLYWOOD (edited August 10, 2000).]