Hi EdFla,
I think what you have is a destroyed one of these:
HEPVO 1-1/2 TRAP
https://www.amazon.com/dp/B00NLMPLDU..._WytNBbDQ92H85
On new units that have these waterless P-Traps, there is a warning sticker on the shower base that reads: Do not use routers to clean the pipe.
So if your drain gets plugged with hair, soap or “other” debris, you have to disassemble to clean it.