Sewage stink in mudroom

[VNMegh]

Hi,

We moved our laundry from mudroom on the main floor to second level but left the plumbing and utility as is in the mudroom. Now after a year or so my mudroom stinks of sewage gas. I tried clearing the utility sink pipes with all sorts of unclogging methods. I don’t think there is any clog but it smells really bad. Please help.

 

[Ben-gee]

Trap has dried out?
Pour some water into the waste to re-fill the trap.