Sig calls for a 1" hole in the firewall for the top of the fuel tank. I read somewhere that some people just run the lines through. Does it matter if its the Brass tubing coming directly out of the tank or should I add the clear flexible tubing to run through?

It's your choice. I modded my Ultra Stick 40 from the 1" hole as supplied, plugged it and drilled two holes the same diameter as the fuel line OD. I doped the holes for fuel proofing, which also closes the holes slightly and makes a tight fit, so less chance for fuel getting past. <div>
</div><div>I also made a balsa 'bumper' glued into the tank compartment which prevents the tank from moving forward during a hard landing (what my pals call a 'crash'), this prevents the tubing from contacting the firewall and pinching or cutting a fuel line. </div>

I do exactly what Eddie does.

Poke a couple of bits of nyrod inner through the firewall to pull the fuel lines through the
firewall as you slide the tank in. - John.

If I use a single hole I make it so the lines just fit through then use silicone to plug it up and keep the fuel mist from getting into it and soaking inside the fuse. I used the clear plastic once that comes in the tank kit. When I tightened the bung it compressed the plastic tubes and almost closed them off. From then on I only use the brass that comes with the tank kit. I usually do as eddie and drill two holes in the fire wall just slightly bigger then the fuel line. Either was works though, just a choice thing.

Thanks for the replies. I hate to start another thread so I'll ask this here also..
I've read that some people use 30 min or longer Epoxy thinned with Denatured alcohol to fuel proof the firewall and I've also read some use Mini-wax Polyurethane.. Is one better than the other? If the polyurethane does work equally well, I'd rather use it just because I have a whole can of it.

The thinned out epoxy will probably more fuel resistant than polyurethane.

With all kudos to mscic and others, I've had better results with poly-u and dope than epoxy. I may have had a bad batch, but the epoxy I used peeled off after several years. Not a big deal, just roughed up the surface again and coated with dope. <div>
</div><div>I also have used Formula U by Pactra, don't know if it's available any more. Sig Stix-It, Balsarite, and K&amp;B Super Poxy also work. Dope does break down with exposure to nitro, especially higher percentages. </div>

I brush on epoxy and hit with the covering gun... ... liquifies it a bit and rotating the fuse allows it to run and seep into all the nooks and crannies... plus it hardens up faster.

Make sure that you fuel proof the inside of the fuse in the tank area - bottom, sides and top. Use the same material used for the firewall. Much easier to do if the fuse hasn't been closed up or there is a tank hatch.

Yep, I'm right in that area of my build. I was thinking I probably should start researching a technique.

<br type="_moz" />

I use an acid brush - nice 'n disposable.

To have, or not have, a hatch is your decision. If I build without a hatch, I make sure there's some type of access to the tank. If it's a tight fit, put some filament strapping tape around the tank and leave extra for a pull. Having a hatch makes maintenance easier, but it better be a snug fit, and make sure the exhaust has an extension to minimize fuel seeping in. <div>
</div><div>The Tango ARF is a good (read: bad) example of how not to build a tank enclosure: fully enclosed, a 1" hole in the firewall for the tank cap, fuselage formers that are tight to the tank, transmitting every vibration to the fuel. It's a fun, goofy plane, but some areas of the design make one wonder. </div>

If you guys get a minute could you look at my Kadet MK II instructions and see what you think of the fuel tank placement? I'm right at the part where I glue the firewall onto the fuse.. I'd appreciate some opinions on this part. So far I haven't drilled the big 1" hole, just two smaller diameter holes , one at 6 o'clock for the feed line and on about 10 o'clock for the vent tube..
edit.. Reason I ask is from what EddieC just posted.. The plans tell me to wedge wood right against the tank.
<a href="http://www.kavanrc.de/instructions/sigrc49kadetmkii.pdf" target="_blank">
</a>www.kavanrc.de/instructions/sigrc49kadetmkii.pdf

edit again... well I guess it does tell me that the blocks can be borken out and not to put them to tight against the tank?<br type="_moz" />

Drill a 1/8" hole thru the firewall and epoxy in a couple pieces of brass tubing. Leave long enough to slide on some fuel tubing to connect the tank and then to the engine as well as the muffler pressure fitting. Works every time for me.

Slow cure epoxy and heat gun is what I use. Do this AFTER you have covered the framework. It's kind of difficult to get some coverings to adhere to cured epoxy.

ARUP - good point as to when to fuel proof the exposed firewall. The inside of the fuse on the back of the firewall and around the tank needs to be completed before any covering is laid out "unless" there is a tank hatch.

I just looked at the manual starting about p.16, and it sounds like you're doing it right. No need for the 1" hole though, since you already have holes drilled for both fuel lines. I'd say it's good. Also, the big hole locks in the tank height, so you lose the option of changing its height later.  The firewall can experience a fair amount of fuel soak in its life, so maintaining its fuel proof integrity is important. The fewer/smaller holes present, the better. <div>
</div><div>Placing closed-cell foam all around the tank is recommended to minimize fuel foaming and thus a lean run. Just don't pack it tight, a little play is fine and makes it easy to remove for repairs and checks. I've also secured the rear of the tank with a piece of hard balsa stick placed diagonally just ahead of the former, then turned/wedged as needed. You can tack it with CA lightly, again keeping in mind the option to pop the piece out to gain access to the tank. </div><div>
</div><div>These are all ideas from everyone here, hopefully you get several to look through and decide what seems best for your application. There's more than one way to skin that cat!</div>

Perhaps you could make a thin ply piece with a 1" hole you could mount behind the firewall, which would support the front of the tank by the tank neck. Then a wood block behind the tank could be secured by screws, so you could remove the tank to replace lines or whatever.

As for fuel proofing a firewall, personally I prefer aerosol epoxy paint. Usually sold as appliance paint at hardware stores.