"Andy Hall" wrote in message
...

snip snip

For the pipework, guesstimate and treat it as a set of cylinders.
Add up the 15mm runs and the 22mm (and other sizes) in terms of length
(two legs remember). Multiply diameter by pi and by length to
determine the volume, remembering to get the decimal point in the
right place to determine litres.

Volume of a cylinder = pi * radius^2 * length (not; pi * diam * length).

At last I've managed to contribute something to this group, instead of
always asking!