The tool I recommend is a dwarven atom smasher.
First, you designate a 1x1 dumping zone
Second, and not necessarily in this order, you build a drawbridge that slams down on said tile.
Upon smashing down the drawbridge onto the tile, you obliterate anything smaller than an elephant (all items and any creature up to a zie of 1200000cm³). This can remove excess items, pets, population, invaders and consequently improve performance.
Note: If items end up being dumped onto an open drawbridge, raising the drawbridge will instead launch the items (and dwarves) in whatever direction the bridge closed.