Where to mount a gas tank

So I want to trade out those stock motorcycle looking gas tanks with a jerry can for my bike, does the gas tank have to be at any position above the tank or can it be level to the tank?
I was thinking of two places to mou t the jerry can, doen by the wheel or on a mount over the back wheel

 

[bakaneko]

2 stroke is strictly gravity fed so it has to be above. The problem with having it exactly leveled is that you will have no slack so if you say accidentally bump it hard or fall then it might come loose. You can also mount your stock gas tank on the rear rack like I did but then you lose your rear rack.

 

[KCvale]

The bottom of you gas tank needs to be above the top of your carburetor, period.
I like this method if you don't want something on your top bar.

 

[HeadSmess]

without any modifications, the tank has to be higher...much higher...than the carb.

you could try one of the perry pumps...vp30 requires a tapped hole into the crankcase.
vp22 just needs to be shaking around a lot...never used one myself...
http://www.perrypumps.com/prod02.htm


a walbro/zama carb, like on chainsaws etc, has a fuel pump built in...you need a line tapped into the crankcase, and the actual model carb that has a suitable EXTERNAL pump line... well, i myself am still confused though, its not too hard to set it up yourself anyways.

if you ever pull the carb of a line trimmer, the tiny hole in the back of it, that lines up with a hole in the manifold...thats the pump line. dont ever block it up with sealant, like most people do!

out of maybe 30 or 40 walbro style carbs i have, only ONE has an external pump line.

and and and, some motorbikes/ride-on mowers use fuel pumps, all with the crankcase tap required. you could be lucky if you go and hassle a few local shops for an old one? sort of thing i would head straight to a scrapyard and probably find within half an hour...