Does your sink or shower smell? Do they talk back to you (gurgle) when draining. I'd bet you have a venting or trap problem that you're not aware of yet. Plumbing Drain, Waste and Vent systems carry away waste while keeping the sewer gas smell from coming back up into your house.
You can read more about the right way on InspectaPedia as I just want to show you some of the
"DO NOT DO THIS" pictures of stuff I've found.
Plumbing Drain Vents & Plumbing Noises http://www.inspectapedia.com/plumbing/Plumbing_Noises.htm#bannertop
Drain piping should always have a smooth interior wall. Do NOT use the corrugated piping you can buy in the hardware stores. It'll gather crud and cause clogs.
Here's some of what home inspectors see all the time. These are examples of what NOT TO DO!
Vertical Traps won't hold water!
The water in the trap is what keeps the sewer gas from coming back into the house. I don't know what the installer was thinking here other than "Hey, it drains. What's the problem?"
Double traps! If one is good, two MUST be better!
Well, not really. The sink will drain slowly and the corrugated drain pipe will gather crud and cause clogs.
Bubba and his duct tape
Bubba brought his electricain friend along on this plumbing job! But duct tape and electrical tape won't hold this kitchen sink trap together very long!
If your sink or shower stink or gurgle when draining, call a real plumber. Help put Bubba out of work!