The tank sits on those PVC pipes to keep it up out of the bilge water that the pumps can't get up (the last drops). I would say they were put in by a PO because the old tank was not origional, it is stamped 1985 (2 years after my boat was made). Another yahoo member (Dick Shaffer aboard Morning Star) had an issue with his origional tank that had a hole in the fuel pick up line. That left him with only a few gallons of working fuel, everything under the hole couldn't get picked up. I don't know if this was a problem with my boats first tank or not... all i know is my first tank was replaced after only 2 years service.
All that info leads me to believe that the pipes are not origional. They aren't fastened in any way, but they don't move around at all. They certainly aren't PSC build quality
. They don't shift around in the bilge though. There is the weight of the tank, plus the security of the tank hold down (for roll over protection) that keeps pressure on the tank and pipes.
I've never smelled fuel in my bilge.
I ran the new fuel lines the same routes that the old lines ran. This was a little tricky because new fuel lines are thicker OD than older lines.
I had the new tank fabricated to the exact dimensions as the old on. This had to be done because the dimensions of the bilge taper down as you go deeper into the bilge, and they taper down as you go aft into the bilge. This makes for a strange shape. I regret that i didn't measure the new tank before i dropped it in, i was excited to get the job done with.
If you do go ahead with this, make a cardboard mock up until you get the size right. I can't get the dimensions now that the tanks in. Also, if you don't like the PVC pipe idea and you are handy, you could build fiberglass stringers for the tank to sit on and keep it up out of the last drops of bilge water.
Okay, here are some pics with quick descriptions. I'll get some pics of the fuel line runs soon, i just can't find any good ones on my PC right now.
First, here is a pic of the old tank still in. Note the wooden brace (there are actually 2, one already out) that holds the tank down for roll over protection. This also holds it snug down on the pvc pipes. There are also 2 pieces of pressure treated lumber that are as long as the tank is on each side of the tank. These keep the tank from rocking side to side. They are cut to match the contour of the bilge walls so everything is nice and tight. Also, note the space to the left (aft). Keep room so you can access the bilge pumps. I have about 6 to 8 inches space between the aft edge of the tank, and the edge of the bilge access. You don't want to tear the whole boat apart just to replace a bad bilge pump. This space also lets you easily access the fuel supply shut off valve (important to kill a runaway engine).
Here is a blurry pic of the new tank. Note the unusual dimensions. It tapers top to bottom and also taper fore to aft. The welder complained about how many angles it had.
Here is a quick one of the bilge facing aft. This shows the 2 bilge pumps, primary and secondary(higher out of the bilge). Also, behind the two elecs is the pickup for the manual whale pump at the helm. The reason I'm showing this is the block that holds the secondary pump up. If one one the pvc pipes does come loose, it can only shift aft about 6 inches before it meets this. So... the pipes can't get too far.
Now for the fuel lines. All i have now is pictures of the where the lines come into the bilge. This pic is facing aft, for reference. To the right(port side) are the vent, pick up, and return lines. To the left (starboard) is the fuel fill. The fill line actually comes down through a hole in the oil drip pan under the engine. Everything is dressed up well when the tank is in.
This pic show where the fuel fill is. I took this to get dimensions to build a teak cubby to cover the hole left by the PO when they replaced the fill hose. This is facing aft, you can see the companion way to the right, and the elec panel over the icebox to the left (where your nav station is in the "A" layout). The fuel vent and engine raw water anti-siphon vent are nearby. So, if you are at the helm looking into the the companionway, the fill and vents are on the fiberglass step up into the companionway, to starboard. I'll get some exterior shots of this later.
I think i covered most of the questions there. I'll get some cleaner pictures of the fuel lines, fill, and vent later.