Drain Pan Question

In a few months I'm planning on installing a new master bath steam shower with a steam generator. I'm trying to think thru some of the pre work prior to the full remodel. In trying to figure out where to put the steam generator I need some clarification on what the drain needs to do for the overflow. I invision the drain for the drain pan similar to a washing machine drain. With a stand pipe, p-trap, drain run on angle with vent. Here are my questions.

1) Overall what is a typical design for a drain pan drain.

2) If the drain pan is never or hardly ever used. How do you keep water in the p-trap?

3) Won't gases come out of the pipe if the drain is never used?

4) What size pipe do I need to use for the drain?

I may have some other questions as I decided where to put the drain pan but right now this has me confused.

Thanks!!

You are looking to put a pan for the steam unit?
Usually with residential units a condensate line is not required as the size of the unit does not produce enough.
On larger units i've seen people pipe it back into the shower under another steam head.
Here is plumbing instructions for a staem unit.

http://www.steamist.com/Downloads/pdf2/229-F.pdf

I'd love to here an answer to this, I have the same question about what the right way to do it is.
I've always seen a trap put in the wall and some kind of drain line from the unit (copper, PVC, etc) dropped right into the trap with no sort of connection. I've asked about gasses coming back up and what happens if a unit failure lets constant flow through that line without getting an answer yet.

washing machine drain pan

that size drain pan would work best....

usually to avoid putting a trap in the system, when they are installed on the second floor, they are ran down to the basement or crawl space....

and dropped into the sump pump or just into the crawl space gravel......


With a Steam machine

you can either run it into the sewer and put a trap
in the line...

its no different than a basement floor drain that get very little water in it....

all you have to do is occasionally pour some water in it
every month or two...


or you can just drop it into the cralw space like a condensate line

Thanks for the answer. That helps alot!