I bought all of the supplies for the sparge arm back in the States and assembled it here in Beijing. We use it last weekend for the first time and it worked great.
Sorry that I switch between cm and inches...
All 1/2inch schedule 40 PVC:
1 Cross Tee - with the top drilled out to take the funnel.
15 cm long arms
.5cm holes drilled every 2cm = 8 holes per arm
We fill the funnel with sparge water and the arms disperses the water. We didn't have any divots and no channeling occurred.
We used to use a slotted spoon to dissipate the the water during the sparge, but this was much more efficient.
We hit 90% efficiency!