First -- you do not need to take the unions apart while in-place... Buy one of these cutters (they cut sanitation hose like butter, with a clean cut and no effort) http://www.harborfreight.com/ratchet-action-hose-pvc-pipe-cutter-39749.html I found them in gray color at Home Deport in the plumbing dept for under $10. If you can reach the hose with one hand you can cut it and if you can make the cut elsewhere you can pull out in sections, unions and all. (If the hose is wire-reinforced you will need to also use a wire-cutter to snip the wire after cutting through the rest of the hose.)

If you need an access port, buy a 4" hole saw and install an inspection port when you're done -- Beckson makes them in all sizes.

If you pull a hose through a blind area you can cut off the tail piece from a sink drain (that is 1.5" OD) and use it as a joiner to a new section of hose, and pull the new in as you pull the old out.

If you use PVC schedule 40 pipe, make sure you buy the Sealand hose barbs, NOT the 1.5" barbs you get at WM (that are too large for sanitation hose to fit).