Fuel tank and water tank vents are accounted for. But I got the starboard one figured out. Its not a vent, its the discharge for the hot water heater pressure relief line. Still don't know what the port side is for. From inside the bilge there is definitely a hose connected to it, but I can follow it for more than a foot until it disappears up top.
Last year I did your exact steps, except I didn't bother blowing out the line on #5. I just held it down as far is it would go after I disconnected it and it drained out. And I didn't do #4, I am pretty sure it drains clear naturally. But certainly won't hurt to blow it out. I didn't touch the shut-offs. Also, I left the hw heater drain valve open all winter and then closed it before I used it the first time in the spring.
Not much else for you that wasn't covered in your other two threads. Jeff has two great points. I bought my '04 last year with a beat up door track system that I am finally going to replace this winter (still slides, but lots of friction is involved now) and a shorted out pump inside the shower sump that caused it to overflow into the secondary pump area. That was an easy fix with a new pump. So, like Jeff suggested, make sure all that stuff works since you may not have known its there and water is involved. If it doesn't work, might be able to get a few bucks off the purchase or make the repair a condition of purchase. Also, if you do decide to follow the spark plug replacement suggestion in your other thread, since you need 16 of them I recommend buying the AC 41-993 platinum plugs (should come properly gapped at .060 right out of the box) from an auto parts store. They are less than $10 each there and will be around $18-$20 each from a marine supplier.
Bought two 1/2" NPT male plastic fittings (the gray ones with all the plumbing stuff) with barb ends from Lowe's and connected a 5/8" (I think that was the size) cheap clear plastic hose between them which I also got from Lowe's. I just used zip ties to clamp the hose to the fitting. Fittings were 36 cents each. Plastic tube wasn't too much more. For the water pump pickup for the pink, I bought a female 36 cent fitting of the same and connected another piece of the same tube to it. For the genny pickup I didn't have enough length of the genny hose when I took it off the seacock, to fit it in the bucket of pink. The clear plastic tube I used for the other stuff fit nice and snug inside the genny hose. So I just stuck one end of it a few inches into the hose and another end into a bucket of 2 gallons of pink and ran the genny until it all got sucked out and I could see pink coming out the side of the boat. I did not fog the genny. I did change the oil, oil filter, the 2 spark plugs, the inline fuel filter, the impeller and the zinc. All those together were about $50 online. For the A/C, I simply disconnected the hose from the seacock, let it drain out, stuck the 1.5 gallon shop vac hose against the opening of the a/c pickup hose, and blew it out with the shop vac in blow mode. Didn't run pink through it, just left it cleared out all winter. Heck, the manual for it says just to disconnect the hose and let it gravity drain. The blowout I did was a bonus maneuver.
You gotta do the bed extension thing and add the 4" memory foam if you haven't. JimFromMD did his as well. It turns the 300DA sleeping into a 320/340 space/comfort level.
