@Diegocorry
Often when there is a -in and an -an version of a verb, the -in is to do the action to something, and the -an verb is to do the action somewhere or toward something.
I was able to google and find a page discussing this very verb:
filipinotutorial.blo gspot.com/2009/03/ar alin-no2.html
That page says:
“Gamitin ang salitang walisin kung ang ibig tukuyin ay ang pag-aalis ng partikular na dumi o kalat.” (Use the word “walisin” if you’re meaning to refer to removing of a particular dirt or mess)
...
“Gamitin ang salitang walisan kung ang tinutukoy ay isang partikular na lugar na marumi.” (Use the word “walisan” if you’re referring to a particular location that is dirty)
Examples from that page:
Walisin mo ang mga tuyong dahon sa bakuran. = Sweep the dry leaves in the backyard. (ang phrase = the dry leaves = object to be swept)
Walisan mo ang ating bakuran. Tambak ito ng mga tuyong dahon. = Sweep our backyard. The dry leaves are piled up there. (ang phrase = the backyard = location to be swept)