I'm gonna install one of these in my gasser. Do you guys use a 3 line set up or 2 line with a t connector in the fuel line?

You can do it either way. 2 line is simpler. I prefer the 3 line just for the reason you have a direct shot from the clunk in the tank to the carb. You have to set up 2 clunks with a 3 line system though. With a 2 line you just need 1 clunk. It's just personal preference

I use a two line installation for the reasons Jim noted above. Tried three lines a few times and didn't much care for it. Like Jim said, personal preference.

Always have used just two lines.  Simple and works well.

I like three lines with two clunks in the tank - - one for fuel pickup (to the carb) and the other to your fuel dot. But, Ihave never tried a 2-line, so maybe I'll have to. With glow engines (in a 2-line situation) I'd worry about pumping fuel into the carb while fueling through your T. I guess you don't have that concern with a gas engine because fuel will not flow into the carb if the engine isn't running (?).

I use 3 lines, but only one clunk. I do not see the need for a clunk in the fill line, which ends in the tank bottom location.
Maybe someone will enlighten me.

I do not like a two line system for the following reason.
 The line from felt clunk to carb should stay clean. This is not guaranteed if fuel is filled to the tank by that line. Lint from the cleaning wad, down to outright dirty fill bottle lines will be disposed of on the wrong side of the felt filter, and is free to travel to the carb.
It's a Murphy thing that can be avoided.

I agree with Pe on this. I used to use two clunks in a three line set up, but have since eliminated the "fill-empty" clunk and line. It's just not needed. Just leave the nipple on the fill-empty line inside the tank short, and don't attach a fuel line and clunk. You only need to tip the plane to the nose to completely defuel, and never a worry about tangled clunks inside the tank.

I use three lines, but one clunk as well </p>

Two or three is personal preferences.
I like 3 and one clink,  helps keeps the air out of the suction line to carb. Not a biggy.
Don't do what I did, place the fuel dots-lines lower that the tank, siphons back out easly.
Makes a mess at times. you smell of gas as it leaks on you.

<font size="4" color="#ff6600">I used a 2 line system for years UNTILL:

<font size="3" color="#0000ff">One day I took off started a turn to the left with a BLING 3D
and at about 70 ft out into my turn and low over the ground
the motor just quite... The cow pasture did major damage
to the plane... was able to rebuild...

<font color="#ff6600">The problem:
</font>
From pulling the fule dot in and out over 250 flights the gas line
split where it goes over the dot causing the carb to draw air
which I learned the motor does NOT like...[]

So now I do a 3 line like "Pe" does with one clunk..
I angel the fill line down...

Walt..</font></font>

Thanks for the replies guys...........</p>

Good Idea about angling the fill line down, don't have to run 2 clunks.

3 lines for me....

one clunk on the carb line...

fill line is brass tube into the tank and then curls down to the bottom
vent line is standard brass tube curled up.....

I don't like 2 line due to the risk to sucking air into the carb exactly as someone above mentioned....

Does it matter if the fill line points up or down in the tank?  I must be missing something.

the only reason it matters is for defueling, so you can drain the tank completely...