I use 19mm hose for my water changes, I set it up with a 180* rigid PVC bend to hang over top of the tank and cut it to the right length for a 50% water change, put an old canister strainer on the end to avoid sucking up any small fish and can now safely walk away while draining my tank without worrying about taking too much out. Only problem is it's so easy I get lazy and every water change I say "yeah I'll vacuum the substrate next time"...
