Mixing phosphoric acid and hypo clear (specifically the sodium
sulfite in it) will produce sulphurous acid which will cause you to
leave your darkroom in a hurry. I have used a final soak in hypo
clear following my usual phosphoric acid sequence with certain papers
that otherwise retain a very slight yellow tinge. On occasion I had
noticed a faint odor, but very faint and not consistently. Over the
past several months I have been working on a project with Dick Arentz
testing and retesting a wide range of papers. Recently we were
running 2 sets of clearing baths simultaneously -- phosphoric for
most papers and hypo clear for the tenacious ones. At one point we
dumped one tray of each into the sink at the same time and were
immediately overwhelmed by very strong acid fumes, which took quite a
while to dissipate. After trying to figure out what was causing the
fumes we settled on the obvious and to confirm it took a bit of each
outside and cormbined them in a beaker. Sure enough there it was.
Dick called up a chemist friend who said we had produced sulfurous
acid.
So, Steve, I think this is not a good idea.
All the best,
Keith