The heater hoses run along the floor under the bow of the boat and dive down into the bilge compartment along side the steering cable and electrical harnesses.
Once in the bilge area I split the hoses so the return from the heater core runs on the port side, and the supply hose runs on the starboard side. This allowed me to run them to the correct side of the engine and keep the installation clean and out of the way. I secure the hoses to the same restraints that secure the wire harnesses and steering cable as they run through the bilge area.
After reading many posts on heaters, I knew a Y-Tube was essential to get optimal performance out of the heater. I installed the Y-Tube in the cooling hose between the raw water pump and the engine. Note this 1 ¼” hose has two wires that are formed in the wall of the hose for extra support. These wires spiral along the length of the hose on opposite side. Cut the hose with a hack saw so you can get thru the wire as well. Another approach is to cut the rubber on each side of the hose and then use wire cutters to get thru the wire. If you try and use a razor blade knife to cut this hose, once the blade gets to the wire it will want to follow along the side of the wire resulting in a spiral cut (picture a paper towel roll when you split it along the spiral seam)