I use a shop vac to clean the sump a couple of times a year. I try to keep detritus from collecting in the sump with powerheads in between cleanings. If you are going to disturb the sand, I would take the sump off line. I would probably leave the sand alone and maybe clean it once a year, or if I thought it was contributing to algae issues. If it was a deep sand bed, I would be sure only to disturb the upper layers, if any.