I have a stall shower and a tub across from it I want to get rid of the stall shower and tub then put a large shower in place of the tub my question is do I have to put a trap under new shower the stall shower has a trap but the tub does not it just goes into the same drain pipe as the the stall shower that has a trap and if I do need a trap can I have a six foot run from new shower and tap into old trap or does the trap have to be right under the shower thanks jim

Hey Westsnip

You want to run a 2" pipe over to the new shower and install a 2" p-trap directly underneath the new shower strainer assembly you will be installing in the new shower. The vent for this shower needs to connect into (and roll above centerline of) this drain pipe within 6 feet of the new p-trap.

You can probably connect into the old vent...will probably find it as you go along.

Let me know if you have any more questions and also what type of custom shower you are considering installing....a few guys online here, including me, have installed tons of them, so get back to us if you want help with that.

For now, I am sending this site to you...check it out..great info. And pics.!

How to Build a Shower Pan (http://www.hoagy.org/house/HowToBuildShowerPan.html)
.

In addition to what MASS points out I want you to know there are special shower pans made to fit where a tub once was installed. I use Swanstone and they call theirs a reto fit.
Swanstone Shower Floor - Home Improvement - Compare Prices, Reviews and Buy at NexTag - Price - Review (http://www.nextag.com/swanstone-shower-floor/search-html)