Pedestal sink installation question

I recently went to my daughter's house (in another city) to install a pedestal sink, along with some other work.

I cannot get the drain going into the wall to quit leaking.

Here's the setup:
There is a 1.5" galvanized threaded nipple coming out of the wall.
I purchased a polished metal P-trap 1.25" kit from the local big-box.
The P-trap came with metal compression nuts with black rubber washers that fit against the galvanized nipple end.
I tightened everything but we still get water from the wall connection when we run the faucet, and it's a good amount of water.
I also tried sealing with teflon tape.

Where did I go wrong?

Leak

You mentioned that you have a 1 1/4" p-trap, but the galvy threaded pipe is 1 1/2". What are you using to make that last connection to the nipple coming out of the wall? It's important that the nut you are using there is deep enough and has the same type threads as the iron pipe. I personally don't like using the metal drain with the black rubber gaskets, because they seem to leak a lot more than the plastic seals do. But polished chrome does look better in open areas.

The compression nuts on drains aren't an interference fit, I don't think...they are more like threads for a hose (they're not tapered). It could be that you can't get the nut tight enough to actually pull the beveled washer tight enough to seal. If you were trying to create a seal with the drain and it was over the threads of the nipple, I doubt you would ever get it to seal. Normally, you'd have a Desanko (sp?) at the wall connection, not a nipple as I understand it.

You may be better off using a 1 1/2" PVC nut with FIP threads to make that final connection.

Thanks guys for the tips. It seems to always be true for me that even the simplest jobs take twice as long and cost 3 times more than I anticipate!

connection

Very seldom is a galvanized pipe smooth enough for a slip joint connection not to leak. A rubber 1 1/2" x 1 1/4" reducing washer with a metal nut will sometimes work, but a plastic nut with a plastic washer seldom will. The proper connection is a transition fitting which goes by various names, (i.e., DeSanko, trap adapter, Marvel connector, waste and vent adapter), depending on your part of the country screwed onto the galvanized and then the trap sealed with the slip nut and washer.