On my B36(2002), the CAV fuel filter located just inside and immediately aft of the engine compartment starboard side door, had two outlets on its aft side. One was used to supply the engine, while the second outlet, immediately next to the first, supplied fuel to the heater. The fuel supply take off point from the fuel tank under the starboard cabin bunk board, entered the tank at a location where it was likely to have access to a deeper point within the fuel tank than one or other of those that you are referring to. My thinking is that this deeper suction point would be better from the heating point of view as it would enable your heater to use as much of the remaining fuel within your tank during the over winter lay up period when many boats are stored on shore. This was my own personal, preference as it enabled me to empty the tank over winter before adding in fresh diesel fuel. It also saved having to make or find an alternative fuel supply for the heater, and mainly because that was how the boat came when I bought it second hand when the boat was about eight years old. Basically if it worked, then don't fix it, and it worked for me, so I left it alone save for those occasions when I wanted to run my fuel polishing system, when I would connect in to that take off point using a new “T” piece and blanking plug that I bought from our nearby hydraulics supplies outlet where they were able to supply the correct plumbing fittings to match the thread sizes on the existing fittings. (The fuel suction to the polishing system would connect into the otherwise blanked off end on the “T” piece).
