Following strict leave no trace principles, you're already doing a pretty good job. Where you can improve is to use no soap, small amounts of biodegradable soap are acceptable, but you can clean your dishes with just hot water. When you're done scrubbing, it's best to strain your scraps out of the water and pack them out with the rest of your garbage, then either dig a small cat hole to pour the waste water down, or better yet fling the water out in an arc to disperse it as small water droplets over a greater area.
If you've dug a latrine area, you could also dump your dish waste in there, but do not dump your scraps in an outhouse. You can pour your dish water out in an outhouse, that's actually helpful, but don't put anything solid in an outhouse unless you're pushing it out after first digesting it. Someone else dug that hole, it's very rude to fill it with anything except what they dug it for.
It's not good to bury anything in sand, because sand is technically a system, not a layer of soil. Soil decomposes, sand does not, sand actually flows, albeit extremely slowly, but all sand eventually ends up at the bottom of the ocean where it eventually lithifies into a new sandstone layer, but I digress...
If you bury your scraps, treat them like the rest of your human waste, bury them in soft soil (under some nice rich humus, right in the 'A' horizon of topsoil, or right on top of the 'B' horizon of subsoil), but try not to disturb any vegetation. Avoid rocks, gravel and sand. Your waste will just end up down stream in the next runoff if you try to plant it in anything but soil.