The easiest thing to clean is actually a bare tank floor, just that some people don't like the look of a bare tank floor.
When cleaning sand, you need to use the siphon/gravel cleaner when you're siphoning waterchanging and run it through (gently siphon) the sand (this should be done weekly) as you'll invariably find bits of waste buried beneath the sand. The siphon can then be gently shaken and the sand will drop back down to the tank floor. Any sand that ends up in the bucket we just empty the dirty water into the garden and scoop the sand back into the tank.
Another reason to regularly siphon the sand during your waterchanges or stir it up using a turkey baster, is that you get pockets of anaerobic gas building up which can cause a water quality problem for your axolotl.
Large stones/river rocks/gravel are actually harder to keep clean, even using an undergravel filter. Waste tends to drop between the rocks and under the filter plate - even siphoning will not completely eliminate the waste buildup which can cause more of a water quality problem than sand would.
You also have to remember when waterchanging or siphoning to check under any decorations between plants or under tunnels that waste will remain hidden unless you move them to clean there.