For the tubing, check Xringer's thread on the airtap A7 HPWH he installed. He successfully integrated a solar/ashp/oil furnace powered water heating rig into his house for hot water no matter what. Last I heard, his solar was doing most all of the water heating, with the Airtap kicking in during high demand. Since the tank was rigged in, he has burned very little fuel oil at all. Way down from thousands of dollars a year.
http://ecorenovator.org/forum/geothe...er-heater.html
Randen also turned a 5000 btu window aircon unit into an air-source water heat pump, with much custom work done throughout. He is just a mechanical master genius. Everything he does comes out looking awesome, even the stuff that doesn't work! I hate to see a good-looking piece of machinery destroy itself, but it looks ALMOST as good dead... kind of like taxidermy.
http://ecorenovator.org/forum/geothe...heat-pump.html
If you look at a larger split-unit install manual, the manufacturers have pictures and guidelines for where and when to put the oil traps in the lines. They work just like a p-trap in a drain. When the flow stops, the extra oil gets stuck in the trap instead of finding the bottom of the plumbing. When flow starts, the oil is carried back to the compressor much quicker.
Rather than jog the line laterally for the trap, you can loop it once for the same effect.
With natural refrigerants (propane, propylene, butane, etc.), the oil is much more soluble and miscible in the refrigerant, so oil flows much easier and better through the system than with "modern"(r134a, r410a, r407c, etc.) refrigerants. As a result, it is usually ok just to size the tubing small enough to get decent velocity, so the foamy froth can make it a decent way back up the tube before the gas and oil separate completely.