Older sprayer used for Roundup

I've got an ATV sprayer that I used a few years ago (7+) for round-up'ing the fence lines at my horse farm. Now the horse farm is sold, and I need a sprayer to apply herbicide to my 1.5 acre lawn. Can I use the old sprayer that was used for Roundup? Is there a way to clean the Roundup residue out? Or, do I need to get a new sprayer? thanks in advance.

Pigdoc