DistinguishedName is a default attribute for Get-ADComputer.
If you just want the container OU, you can split the distinguished name via the following method.
(Get-ADComputer computername).distinguishedName.split(',',2)[1]
This splits the distinguisedName into two parts separated by a comma, and then returns the second element in that array.
The information before the first comma is generally the canonical name. (CN=).