What is the best way to rebuild this shower drain?
You should cut the 2&quot; main line (at the location shown in the first picture) and rebuild the assembly entirely, eliminating the combi (reducing tee) and any 1 1/2&quot; components and orienting a new 2&quot; sanitary tee to the correct angle to line up with a new 2&quot; trap located directly under the shower drain. Why on earth would you reduce to 1 1/2&quot; here when you could very easily make this all 2&quot;?