If it s too long cut it with a hacksaw.
Bathroom sink tailpiece too long.
Then cut tail piece accordingly.
Cut the extension to the proper length.
Tail piece should be long enough to be fully inserted into p trap and seal.
Trim the tailpiece to fit.
New tailpieces come quite long so they can be trimmed to fit.
You doing this for measuring purposes only.
If it s too short add a tailpiece extension which is a short length of pvc pipe.
If the tailpiece will not line up with the trap move the trap into its original position tighten the collar with the pipe wrench and obtain a flexible tailpiece extension for your drain.
This bathroom sink tailpiece too long graphic has 20 dominated colors which include uniform grey silver tin cab sav steel pig iron sunny pavement thamar black kettleman snowflake black white benthic black driftwood bengala red honeydew rusty nail foundation white himalayan salt ivory.
There is lots of play so no worries.