Eigenvector wrote:
My bath drain, drains very slowly. It doesn't appear to be clogged with
hair

Just curious, how do you know that?

and it drains into a septic tank. No other drain seems to have a
problem. However I was wondering if the way the previous owner routed the
drain lines might be the source of the issue.

http://photos.imageevent.com/eigenve...e/P9160042.JPG

Shows the drain. There are two obvious things that make me wonder. One, as
you can see there is a wierd PVC joint right above the transition to the
galvanized pipe - almost like they necked it down, you can see all the green
joint compound. The other is the absolute horizontal pipe that runs from
the tub drain to the PVC "T" junction. Could this be the source of my slow
drain?

I would say no, the section past the P trap seems to slope well but I
can't see what happens after that.

I presume the vertical PVC pipe section is for the tub overflow
drain - it doesn't go anywhere else and it isn't a vent so far as I can
tell.

Yes, should be the overlow

A couple of questions, if I were to snake the tub drain, would the trap
cause problems

Shouldn't but it's always better to be very gentle when snaking old
pipes.

Another think you may want to check is if that drain has a dedicated
vent pipe http://en.wikipedia.org/wiki/Plumbing_drainage_venting and if
that pipe is clogged. Birds, wasps, bees. etc have a passion for those
vents.

Second, if I were to redesign the tub drain, how do I deal with the sewer?

Not sure what you mean here.

I presume that there is basically raw sewage all the way to the top of the
tub drain "U" trap.

Actually no, that pipe should be empty when not draining water from the
tub. Only the lower part of the trap should hold some grey water, but
no sewage.

Should I crack out the NBC suit and call in the EPA or
are there alternatives to dealing with the sewer line?

No, and no need to call the cavalry either. If you re-route the pipe
(why?) or replace it, just stuck some rag on the septic side to keep
the odor down until you'ready to reconnect. You don't want that rag to
go all the way inside the pipe, right? No offense, but replacing that
drainage pipe is a job is better left to a pro.

BTW: I finally cleaned out the bulk of the spiders in that corner, as you
can see its relatively clean now. The webs back there made the opening
scenes of Raiders of the Lost Ark look like Martha Stewart dusting cobwebs.

Now you have some very p...d off spiders there.