On 9 Apr 2004, Rod Hewitt wrote:

I think that you will find the word used was RESIN not residue. The water
softener uses a special resin that looks like coarse sand but slightly
transparent like poor quality amber. (I am sure that there is likely to be
considerable variation in the precise look of it depending on brand, age,
etc.) This is usually in a container that is accessible from the inside of
the machine via a small hatch or screwcap and sits underneath the floor of
the main compartment.

Thanks for this informative reply to the question I asked in my original
message.

Ron