I could probably write a book just on all the hoses used... there is a lot to know about each one individually but I'll start with some basic info. A few are still available but most are either NLA or prohibitively expensive for the casual time machine builder. I've spent more time than I care to admit running NSN searches to find hoses that are close that can be cut apart and made to look correct. Most were originally purchased from Luky's in Burbank, CA. This place can still cut and crimp hose ends so if you find hoses with the right fittings but are too long, or only have one correct fitting you can frankenstein multiple hoses into one good one.
A while back I was talking with another member on the board and he created this image of the rear deck and assigned letters to each hose:
"A" - Hydraflow Bulkhead Hose(s) - These can be purchased to original spec direct from hydraflow. Super expensive though...like 300 bucks per hose. Need one on the side of the car and the same hose is mounted next to the flux capacitor in the inside of the car. The end fittings and crimping ferrules have slightly changed over the years but are pretty much the same as vintage hoses.
"B.1 and B.2" - Vent to Bulkhead - Large hoses from the side of the vents to the bulkhead are different PN's for each side. These can still be made to spec from the original supplier, I don't have the info handy at the moment for the supplier, but if you're interested I can dig it up. I think each hose was a couple hundred bucks.
"C" - Hydraflow Janitrol hose - This simply inserts into the Janitrol and the other end connects to a custom welded pipe fitting/bulkhead connector that is screwed into the bulkhead. The hose itself is similar to hose A but is a larger size. Same green nomex casing over the hose.
"D" - Flexible Aluminum Duct - Can be purchased from NAPA and other auto parts stores, pretty standard emissions hose.
"E" - Oil Separator to Trapezoid Hoses - These have to be hand made from scratch and are a huge pain in the ass to make correctly. Metal flexible inner hose covered by a special SS woven double outer braid. We've had to machine end fittings from scratch since they are not available anywhere.
"F" - Weatherhead crossover tube - Used to be plentiful at Luky's but have not been available for a long time. People have made castings of these that look just as real as the originals. The end fittings can be painted with "Metalcast" anodizing paint.
"G" - Vent to Vent - Small black inboard hoses w/ 45 deg fittings that bridge across the black strip on the vents. These also came from Luky's and no longer exist. The set I have was custom made by butchering together various different hoses that had the correct end fittings.
"H" - Reactor Duct - Black corrugated ducting connected to plastic/PVC elbows painted silver. Each requires a different type of clamp. Lots more to know on the hose and clamps. If you want accuracy.
"I" - "Vent to Deck" - Small stainless hoses with 90 fittings originally came from Luky's. These don't exist anymore either with the correct type of end fittings. The set I have was butchered together using longer hoses with the fittings cut off and then crimped back on a shorter hose.
"J" - CAT Ducting -
http://www.aircraftspruce.com/catalog/appages/cat.php - I'll have to look up the correct size. This same ducting is used on the interior of the car along the center console.
"K" - Orange and black exhaust duct - Connects to 90 deg elbow on flux capacitor through the bulkhead.
OTHERS NOT LABELED:
Hydraflow reactor hoses - These are the four reactor hoses that connect around the ring of the reactor and fit between the heatsinks. The far ends connect to the oil separators. These can be purchased from hydraflow or XRP to specs that are close to the originals. $100-$200 per hose though. Vintage ones are almost impossible to find in the the correct size, AN-5 so AN-6 reproduction are one option. The correct hoses have a single black spiral tracer that runs the length of the hose, the repros are either solid green or have a double yellow tracer.
Orange tube - Connects Janitrol to Zero can on rear bulkhead - Flexible Air intake duct. Not sure if the supplier for these have dried up or not.