If you want to measure breast size, here's an easy way that I thought about. The water displacementmethod may be the best but you really don't have to measure the water displaced from a container after the breast is put in to get an approximate weight.

Step 1-- Find a container into which Cathy can place one of her breasts which will fit the breast with room to spare AND where the edge will be against her body.
Step 2-- Fill said container with water and weigh it. This is WEIGHT 1.
Step 3-- Take container and have Cathy put her breast into it such that the water is displaced and the edge is against her body. The container should only have water and breast in it i.e. no air. Cathy may need to be in a prone face-down position to accomplish this.
Step 4-- Here's the tricky part. Carefully remove said breast from the container WITHOUT spilling any water. Re-weigh the now partially full container of water and get WEIGHT 2.
Step 5--Subtract WEIGHT 2 from WEIGHT 1 to get the weight of displaced water which should approximate the weight of the one breast. As someone (I think Steve) commented, you could multiply by 0.9 which may be a bit closer to the actual weight.
Best of Luck,
Matt Zrada
215-500-4934