bathtub drain pipe

Went under the house to check a warped board, found this. The top pipe is PVC and is connected to the bathtub. It is not draining properly into the pipe below it. What is the best way to go about fixing this. I just bought this house back in September. It would be a DYI due to low funds right now.

In a condo apartment I'm looking to DIY reno my whole bathroom and replace my tub. Upon closer inspection from inside the opposite wall where my water main is, I realized the Tee fitting leading to the main drainage pipe is embedded in the concrete. I would like to avoid cutting the concrete...

I've recently replaced the whole bathtub drainpipe from the overflow to the bathtub drain flange assembly. I used schedule 40 PVC pipe, and all has been well until I found a tiny leak, shown in the images below (I will try to get a video clip uploaded, but my file is too large). I had to cut...