I`m not sure about sand or gravel now ,was going to have sand for my corries ,[even bought it ]but worried about keeping it clean, with gravel you can really clean it with a gravel vac ,but with sand it goes in the bucket,you need to hover the vac over the sand ,although i saw a battery vac ,which collects the debris ,so this might help?Would be interested to hear all of your opinions though?