How to keep a flask submerged in water? I am trying to keep a 1000 ml Erlenmeyer flask submerged in a deep cooking pot filled with water. I tried tying the flask to a metal plate, but it was too light unfortunately.

Is there a purpose built piece of equipment for this or a commonly accepted method?
The vinyl coated lead rings suggested in the comment are a great solution. They are, however, expensive and take time to order. There is also the cost of shipping.

A quick and less expensive route is to use a PVC flange and attach what ever heavy metal you have (steel, cast iron, lead fishing weights). Epoxy to flange or drill holes and tie. You may want to paint the metal to avoid rust or other reactions with the metal.  

Home Depot has inexpensive 3" flange or 4" flange.