The simplest equipment needed for this demo is: A piece of aluminum with wire support, a spring scale, and a large beaker full of water. A sample setup with a 1000 ml beaker is in 302-Cabinet D. The 500 cc mass weighs 1.35 Kg in air, and .850 Kg in water. Unfortunately, both the beaker and the aluminum block often are pressed into service for other purposes, so check ahead of time!
A more complete demonstration is provided by placing the beaker on a pan balance, and noting that the upward force of the water on the aluminum (i.e. the reduction in apparent weight) shows up as an apparent increase in weight of the beaker full of water. Suitable pan balances can be borrowed from room 403. The following picture from "Physics Demonstrations Experiments" by H. F. Meiners show how to do it with two conventional balances, but a spring balance is a better choice to suspend the aluminum block unless very high accuracy is desired..