I would not even bother using conduit, mainly for one good reason, it is not waterproof. I guess if you use all plastic type conduit and glue it up your ok.
I would just buy some 1/2 black plastic drip irrigation line, feed the cat 5 cable through that and then bury it. That will be water proof for many years underground. You would probably not have room to run any other cable inside it, but if that is not an issue, that is the quick and cheap way to do it.
If you are worried about what is legal call an electrical contractor and ask or city/county building code enforcement, me, I would just do the 1/2 black plastic drip line. It is cheap and it also will do large radius bends so if you even have to pull the cat 5 out and run another cat 5/6 cable for what ever reason, you should be able to do it.
As for using direct burial type cat 5, I would not bother. Even regular cat 5 will last for many years tacked on to the outside of a house. Placing this type of cable inside a plastic enclosure such as conduit or the plastic drip line will give it enough protection to last 20 yrs.
To get the cat 5 through it, get hold of an air compressor and a cork or even a small section of cloth that will fit into the plastic tube, tie a very strong nylon string to it and feed it into the tube then get the air nozzle and form your hand around the end of the plastic pipe/tube and seal the air nozzle to it, then put the air to it but slowly as if you blast the air it could blast the string in too quickly. It works best if some one holds the string and controls how fast it feeds in to the tube so the string does not feed in too fast and cuts your hand.
Bob