Hello
Recently my brother in law and stepfather have replaced tub on second floor in our house.
Here is the whole story. We used to have a bath there and now they've decided its old and change it to something fancy.
New shower/tub has no overflow pipe, it has only drain.
The drain pipe was also moved about 4 feet away from original one.
Now water drains very slowly and actually when water is on drain can't keep up and shower/tub fills up with water.:confused:
What I've found out is that the trap from old tub was left in place but they put a new one under the new shower, now piping looks something like on image below.
I've read a few topics on here and elsewhere. I am pretty sure I will tell them to remove one of traps that for sure :)
Could it be that not enough air ir getting there because of poor ventilation?
How can we solve the problem ?

Could it be that not enough air ir getting there because of poor ventilation? How can we solve the problem ?
BINGO! Ya don got no vents mon! No wonder your tub drains slow. According to your drawing the tub's double trapped, (code violation#1) It's not been vented, ( code violation #2), there's a "S" trap on the lavatory, (code violation #3) and on top of all that the one thing left that could possibly vent the tub, the overflow, you don't have on the tub.
The solution is to tear out the existing drainage, get a plumber in that knows what he's doing, and do the job right. Good luck, Tom

Thanks speedball1

If lets say I remove one of the traps and add pipe under the tub, as if it was overflow. Would that help ?
Something like that:
http://img223.imageshack.us/img223/8981/bath2uy9.jpg

I'm confused. If you remove the running trap you would still have a "S" trap on the lavatory. Were does the toilet connect to and is it vented? Can you put up a more detailed drawing? Let me show you a typical bathroom rough in. Most bathroom groups are roughed in like this.
Toilet connects to sewer main or the stack vent. Lavatory connects to toilet drain and runs a vent off the top the stubout tee out the roof or revents back into a dry vent in the attic.. The toilet wet vents through the lavatory vent and the tub/shower connects to the lavatory drain and is wet vented by it. This is a normal rough in and is acceptable both by local and state codes and also The Standard Plumbing Code Book in 90 percent of the country. Check your local codes.to make sure you're not in the excluded 10 percent.. The vent off the lavatory may be run out the roof or revented back into a dry vent in the attic or if you're reventing back into a fixtures dry vent you must make your connection at least 6 inches over that fixtures flood rim.
Let me hear from you, tom