On Tue, 24 Mar 2015 17:40:37 +0000, Tim+ wrote:

More likely either (a) fatty solids from the items being washed or
(b)
a problem with the drainage.

I would have thought that dishwasher detergent would be most unlikely to
congeal.

So would I. I'm under the impression that dishwasher "detergent" is
pretty caustic stuff . You certainly don't want to hand wash your
dishes using dishwasher detergent...

As Nick says, most likely to be greasy plates. Lamb fat in particular
is great at setting in drains.

We need a description of the stuff that is blocking the drain.
Washing machine powder has been mentioned that clogs the pipes with a
hard but crumbly residue. Fat is fat thick softish stuff with not
much texture.

Any drain that regularly needs to be rodded has a fault or is having
stuff down it that shouldn't go down it, like animal fats. "Fault"
would normally be not enough fall so solids don't get carried by the
water flow or too much fall so the water flows away too quickly
leaving the soilds behind.

--
Cheers
Dave.