Bathroom Sink Remodel/Drain Pieces Aren't Long Enough

Hi all,
I am the epitome of Plumbing Newbie. That's right - my very fist plumbing job. Please hold your laughter til the end...

Recently, I put in a new sink and faucet into my bathroom. Hooray for me! ....almost. I went to reconnect the pipes underneath, but they don't fit.

There is now a gap in between the u-shaped trap and the straight drain tailpiece.

I found something called an "extender piece". It's a 1 1/2" straight plastic piece that looks like if I cut it a bit, it will work. I just don't want to be running back and forth to the hardware store the rest of my life to get this done.

What part do I need to buy to finish the job? I can't have guests washing their hands in the bathtub.

extender

Depending on the opening in the trap, you either need a 1 1/2" or 1 1/4" slip joint extension. Buy the right one and cut it to fit.

Most bathroom sinks use 1-1/4", but to be sure, just take a piece of the existing drain with you to the hardware.

Once you figure out what you need, you can cut it using a hacksaw. You can hold it in place with any mitre box. Also, some toolboxes have a groove on top where you can clamp down a pipe with one hand and cut it with the other.

Don't cut it too short. You need to leave a little extra to insure that it doesn't pull out and leak later on.

Slip joint extension....never would have figured that one out.
I'll take the stuff with me to get the right fit.

Thank you!