In previous projects I really haven't had the need to dry assemble a
bunch of fittings to get the alignment right and make sure it would
all work before gluing. In the case of some recent work with 2" PVC
I had pipes making a tight 180 turn and together with a 3 way valve,
it all has to align just right with the existing piping in a short
distance with no wiggle room.

So, I put the pipes and fittings together dry first, to make sure they
aligned OK. But there were two problems:

1 - It was very hard to get the dry pipe to bottom in the sockets of
the fittings

2 - It was even harder to then pull them apart.

I tried using some dish washing soap, but it didn't help much. Which
got me to wondering if there are any tricks the pros use?