My Plumber, Stinky, refuses to do any sort of Empty Pipe jobs. I have tried having the Tidy job priority maxed and disabled any other possible jobs he might do (just does other tidy jobs instead) maxed the sub-priority of the pipes (still nothing), turned on Advanced Mode and walked him to the pipes are (walks away to the next-closest job) etc... The *only* scenario I've found where he actually empties the pipes is when I wall him off in the same room as said pipes... and he will still do all other possible Tidy jobs before going for the pipes.
Steps to Reproduce
Make a dupe a plumber. set a empty pipe job. Try to get them to empty pipes.
This issue has been fixed in either a future version or updated in a previous version.