Why did the drain run so slow???

We were up early this morning as we wanted to get a start on the guest bathroom. We had a quick breakfast and off we went. We started with the toilet first. It was a little hard trying to line up the bolts but we finally got it done. I had to run to Lowe's to get a shorter water hose. I only needed a 6in piece and all we had was 20 inches. So off I went. Once there I found everything I needed. Beth started painting the doors the blue color. It looked really cool and so tropical. We got the toilet all hooked up and turned on the water. Finally a project that does not leak. Beth is so happy to have the toilet up and running. So I moved on to the sinks again. The right one had one little drip but after some plumber's putty the drip stopped, but it seems to drain out very slow. On well at least it is working and no leaks. About that time Dawn came by to drop off Rylee. She had a class to go to and then would be back. No problem. We love watching the princess. She played in the exercise saucer for about an hour, She was able to turn it all the way around even thought she did not know what she was doing. She was starting to get a little tired, so we tried rocking her and walking with her get her to sleep. She was having no part of that. She started to scream and cry real tears. It was so sad, so we made a bottle and she only drank about 3 oz. before falling asleep. Dawn called to say her class was cancelled and would it be alright if she went to the mall. I told her no problem and to take her time. Rylee seemed to have baby bad dreams and would cry but her eyes would be closed. We laid her on her normal spot on the couch and she was fine. Dawn came by about the time of first pitch of the Phillies game. So she stayed to watched it with us. She had ball practice and had to leave around 4:45pm. Rylee was still sleeping, so we gently put her in the car seat and off they went. After they left, we watched the Philles lose and worked on the bathroom so more. I drilled the holes in the tile to hang the curved shower rod. I was so happy that I did not crack any of them. So one more thing completed. So back to the sink. After one more taping and tighten. I found the pipe was fine at the joints, but had a crack in the side of the pipe. Just great. So I had to unhook all the pipes and turn the water off. The pipe is the one that goes into the wall. It was easy to get off, but to my surprise I found out why this sink also ran slow. As you can see from today's picture the pipe is 3/4 the way clogged with crap. No wonder is runs slow. I am guessing that is why the other drain is slow also. So off to Lowe's I went to get a new pipe. I ended up getting 2 and once the one sink is fixed and all done I will pull everything out and check that pipe. I want to get it done now and hope to never have to do it again. So Beth painted the vanity front and I will fix the drains tomorrow. We did replace the shower head. So things are getting done and the end is in site. Guess these things happen when you replace 40 year old things. I hope to have both sinks completed tomorrow. Then it is shopping time for accessories.