I am preparing to replace the drain and piping in this old house but I can't figure out how to unscrew the old piping. Take a look, please. [attach]107344[/attach] [attach]107345[/attach]

Sadly the previous owners of my current home may have done things incorrectly in many places. I'm not sure if the drain to the whilrpool was done right as indicated by the backflow I'm discovering when heavy drains from the washing machine or dishwasher gets ran. We pour our coffee grounds down the drain in the kitchen. This has helped scrape the drains of years of buildup and keeps the garbage from the chores of messy coffee grounds. Unfortunately, these grounds end up getting deposited in the tub when the backflow occurs leaving evidence of this problem. The second giveaway that something is awry is the nasty smell of what can only be described as acidic decaying vomit in the air. Is there any way to detect if there is an improper drain setup for this tub and what can I do about it?