John Stumbles wrote:

OTOH if the pipe you're teeing
into is neatly positioned in the middle of 3 run side by side then you're
stymied as you can't tighten the nuts on the compression fitting.

Strap wrench, chain wrench will do this on a compression fitting. All
you have to do before hand, is compress the olives on a dummy pipe
fitting and then fit them in situ, using a strap wrench to tighten them
up :-)

HTH

Dave