Posted for Mark Steitle <msteitle@mail.utexas.edu>:

David,

Sorry, what I have been referring to as an "expansion tank" is actually a
"purge tank".   My purge tank looks like the one in the picture that Paul Connor
posted yesterday.

It also has a connection just below the cap for a small 1/4" line.  I've connected
that to an "expansion tank".

Sorry if this has caused any confusion.

Mark S.