We have a pedestal sink and a week ago the pipe that goes into the wall fell apart. It had rusted through. I got the replacement parts (all metal parts) at the hardware store. The pipe that goes into the wall screws into the pipe and has a plastic washer. It sealed tight - no problem. Then the P Trap screws into the pipe that goes into the pipe that goes into the wall. Same thing - the P Trap screws into the pipe that goes into the wall and there is a plastic washer. Those two screw into each other and they seal tight. Then the P Trap just slides over a metal 6 inch piece that is over the plastic tail pipe that goes directly up to the basin underside of the sink. This P Trap has a screw cap on the part that slides over the plastic pipe to the basin but I have tried plastic washer and rubber washer and I have made sure I hand tightened it and then a quarter turn more, but after 10 tries it still leaks water out of this part, which is the only part that does not screw into another pipe. What do I need to do? Please help!

I have read this 3 times... can't picture it! Lol
Can u post a pic?

I think I have it whittled down to where the solution would be. The tail piece that comes out of the underside of the bottom of the bathroom sink is plastic pipe. Then there is a small 6 inch piece of metal tail piece pipe attached (leak free) to that plastic straight piece of pipe. So I am attaching the p Trap to this 6 inch extension tail piece. And when I slide the cap and the washer up the pipe and then hand tighten the cap piece down on the P Trap piece I can still wiggle the P Trap up and down the pipe. So it is not "clamping" or "squeezing" tight enough to be water tight. And I know I have the right parts. What can I do?

Many of those drain pipes are actually 1 1/2" pipes but have washers that will also reduce them to 1 1/4" Are you possibly using the 1 1/2 washer on the 1 1/4" pipe?

Bobs answer would be my guess. Are you possibly using the 1 1/2 washer on the 1 1/4" pipe? Regards, Tom