Geoff & Heather wrote:
George,
What about 19 or 25 mm black poly pipe (depending on diameter of existing WM
hose. 91mm Poly pipe ie standard irrigation pipe is really cheap

Errr, no. AFAIK, that 19mmm cheap stuff is definitely NOT standard
irrigation stuff. It is thin wall stuff for the home market. It is okay
for low flow, low pressure situations, like trickle watering my vege
garden beds from 2m high tanks via a 19mm backbone around the fence

The really good stuff is much thicker, stiffer and expensive.
Unfortunately, I needed to buy it to join my two tanks for storage
balancing (aka the small one collects more water than the large one)

For his application, unless his washing machine feeds into a surge
tank[1], then he definitely needs a pipe FAR bigger than the outlet to
the washing machine. There must be a physical break so that atmosphere
comes in and allows the WM pump to run as designed.

The outlet on our washing machine is actualy 19mm internally, but it
would be unwise just extend the pipe as the extra 20 metres of pipe will
increase the resistance to flow by about 11 times[2], which is
something the washing machine water pump is not designed to handle.


[1]Another idea for a surge tank might be a vertical strip of 90mm
stormwater pipe (an economical buy) against the wall. You would need to
buy an end cap and glue it on, then glue/bolt on a hose socket at the
side on the bottom. Put a brick on the ground and sit the endcap on it.
This takes the weight. Hold in place with a couple of pipe brackets. You
could even paint it to match the wall. It is an effective surge tank and
as it fills up it, increase, the flow through the 19mm pipe or hose to
the garden lawn.

My rough calcs says that a 2m length would hold about 12L (YMMV[3]),
which should AFAIK be adequate for the general domestic washing machine.

[2] Actually,the volume of flow through a 22 metre pipe is 1/11 of the
possible volume through a 2m pipe, all other things being equal.

[3]3.1415x0.045x0.045x2000 = 50.08 L