[Shop-talk] Pedestal Sink Trap

[Peter J. Thomas]

I've demo'ed the powder room.  Replacing the vinyl with tile, the vantiy 
with a pedestal sink and going to add wainscoting.

The problem is the waste line for the sink.  Originally the P trap went 
out the left side of the vanity tied into a 1 1/2 inch vertical stack 
which is the vent stack above the junction.  I believe this is also the 
vent for the toilet as the 1 1/2 waste line ties into the end of the 
toilet waste line.  The reason it went into the side wall instead of the 
back wall is because there is a joist underneath the back wall.  Putting 
the sink against the side wall is not an option, I must to against the 
back wall.

So what to do?

Option one is an S Trap.  Pretty sure it won't siphon the trap  It's 
just a powder room sink and there aren't any fixtures upstream.  But S 
Traps are against code.  Also I can't find a "Pedestal Trap", so the 
pipe would be exposed against the back wall.  I can't put it in the wall 
because of a joist underneath the wall.  Any one know of a source for a 
"Pedestal Trap".

Option two is to use a P Trap in the back was with a 1 1/4 vent running 
horiztonally through the wall, tied into the original.  For a 1 1/2" 
drain I only need 3/4" but code says a minimum of 1 1/4" for the vent.  
None of the walls are load bearing. So I believe the would meet code.  
Still the pipe can't go completely in the wall because of the joist below.

Option three is to put the trap in the floor.  Straight pipe down 
through the pedestal and a small 1 1/2" P trap in the floor.  I actually 
like this option the best but not sure it's legal.

Any sights?

Peter T.