The command Kappy gave you is a perfectly legitimate one. But even Apple, who suggest using it, point out that it may be dangerous if not entered absolutely correctly. Just be sure you only copy/paste it in. There is absolutely nothing obsolete about the cited article.
What might be going on when you get the message no valid sudoers is you are running out of a standard account, not an admin one and you must run this command from an admin account. Some things to try. You can go into Accounts (or Users and Groups) and change the standard account, either temporarily or permanently, to an admin one. Or you can create a new admin account (it must have a password.) Or if you already have an admin account--or if you create a new one--you can run the following command first before trying the command Kappy gave you. This next command would temporarily give you the privileges of the admin account and enable you to use sudo.
su <short name of admin account> or if that balks use a hyphen
su - <short name of admin account>
Note, there is a space after su and the admin account name, or after su and - and then after - And also note, if this isn't obvious, do not include the < > when entering the short name of the admin account. This is unlikely, but if the short name has any spaces in it, the name must be enclosed in quotation marks. You must use the short name for the account which has the Trash problem.
Hit return. Then give the password of the admin account when prompted. Next enter
sudo rm -rf ~/.Trash/*
And then give the password again of the admin account. When finished type exit, hit return and then just close the window.
Then log out and back in or restart.
This may avoid needlessly reinstalling.