[CentOS] Scripting help please....

Need a scripting help to sort out a list and list all the duplicate lines.

My data looks somethings like this

host6:dev406mum.dd.mum.test.com:22:11:11:no
host7:dev258mum.dd.mum.test.com:36:17:19:no
host7:dev258mum.dd.mum.test.com:36:17:19:no
host17:dev258mum.dd.mum.test.com:31:17:19:no
host12:dev258mum.dd.mum.test.com:41:17:19:no
host2:dev258mum.dd.mum.test.com:36:17:19:no
host4:dev258mum.dd.mum.test.com:41:17:19:no
host4:dev258mum.dd.mum.test.com:45:17:19:no
host4:dev258mum.dd.mum.test.com:36:17:19:no

I need to sort this list and print all the lines where column 3 has a
duplicate entry.

I need to print the whole line, if a duplicate entry exists in column 3.

I tried using a combination of "sort" and "uniq" but was not successful.
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