I'd have to say something is really very wrong with the tank.  Maybe it was "modified" incorrectly by the airplane builder who didn't understand how it was supposed to work.  It also is possible it was assembled incorrectly from China.  I've heard of a couple bloopers from those particular tanks,  or perhaps it was purchased in kit form and just assembled wrong.  I doubt there is any real choice but to replace it.  It would never work as is except perhaps to fly only level upright-and always started that way.  Also if you DO replace it go with a uniflow style instead of straight suction like yours appears to be.  These give a more even engine run start to finish and therefore don't prematurely wear the engine out with screaming runs as the tank gets close to dry.

Dave

That should be right.  The one furthest from the wedge will be the overflow which will be capped off after you fill the tank.  It's best to install a couple of copper tubing stubs through the fuselage to connect the uniflow and over flow tubes to with fuel line.  It is also good to have the foreword end of the uniflow inlet tube outside the fuselage to be above the fuel level in the tank so that fuel doesn't run back out on the ground after you fill.  You can either penetrate the fuselage higher up or use a longer piece of copper (brass corrodes very quickly in nitro) that turns up and then forward into the slipstream outside the fuselage.  The overflow tube location doesn't matter much.  A good way anchor these is to slip a #4 washer over the tube and solder it where it penetrates the fuselage inside.  You can then epoxy or JB the washer to the inside of the fuselage.  I build my tanks so in most cases I just have longer tubes soldered into the tank and they just go through an opening to the outside but the idea is the same.  I'll post a photo shortly so you can see what I mean.

Dave

Not to confuse-  you see another short stub of tubing in the cowling just ahead of the tank tubes.  This simply allows me to connect a piece of fuel line to the uniflow line and “breath” air from inside the cowling when the wind is strong so to eliminate the engine going rich into the wind and lean downwind.  It works very well for engines .45 or less.  In these big ships of mine (RO Jett .76) it seems to not quite get enough air in the tank to replace the fuel drawn so the run can get progressively more lean as the flight goes on so I’m not sold on it for the bigger planes .  Works sweet on my classics with Fox .35s and Max S .35s though.

Dave

Not quite the same thing, but the test can be used here.

I keep a piece of lawn mower throttle cable, a bicycle brake cable and a transmission/speedo cable (all sans exterior sheathes) for probing automotive and motorcycle fuel tank vents. I can usually find the inside/open end stuffing the springy wire into to the tank and feeling/listening-to the exterior for "tap, tap, tap."


Another trick is to submit a few cc's of rubbing alcohol into the tank, and then try to suck it back out while rolling the airframe around each of the axis. The alcohol goes to "bottom side," and the other end of the line will become submerged and sucked out. Now you found your pipe end. This may take several iterations with varying levels of alcohol.

I hope this helps mapping out the tank lines.

If you haven't done much work with the copper tubing ( 1/8" K&S  from Ace Hardware) then you'll find it quite hard to bend without first annealing it.  I run it slowly through the flame of a propane torch until it nearly glows red then let it cool naturally.  Then it will bend well without kinking.  You can also lay it on the burner of your stove for a while,  moving it around to get it all heated.  This works well until you set off the smoke detector........Once that is done sand off the black soot from the outside to clean it for soldering.

Dave