This article is for following cases, when the Finder app doesn't remove files from the trash with a following exit message

The item cannot be removed because the item "{item name}" is in use

For this case, there are two solutions - SIP method and Safe Boot method. Note that you need to try the SIP method first, but if this doesn't help, go over to Safe Boot method.

SIP method

In this case, you need to disable SIP (System Integrity Protection).

To do this you need:

1) Restart your Mac with holding Cmd+R

2) After you get to Recovery, click Utilities in Menu bar and select there "Terminal".

3) When the Terminal window is open and you see a blinking cursor, type ...

scrutil disable

... and hit Enter

4) After you see updates in the Terminal window, restart your mac computer by clicking  > Restart and try erasing the Trash.

Safe Mode method

1) Hit and hold the Shift button on Power Up

2) Open Trash and try erasing it

3) After the Trash has been erased, restart your Mac without any keys holding.