Even if you pull the plastic tube, you won't get more than about 38 liters (8.5 Cdn gallons) in an Apex from the point where the sled is quitting every time you try to accelerate. Without pulling the tube it more like 35 liters or 8 gallons.
There is a huge reduction in fuel range between an 05 RX-1 and an Apex.
In some of my old posts I talked about getting 177 miles to a tank on an RX-1 riding normally, yet I'd be lucky to get 120 miles with the Apex (taking it easy in ideal hard packed conditions).
Also with my RTX I've run it basically out of gas in 80 miles when riding hard. My buddies 06 Apex ER gets even worse mileage than my RTX by 5-10% too.
I still don't understand why no-one has offered an auxilliary fuel tank for the Apex chassis. With an extra 10+ liters/2.5 gallons, these sleds would have a very acceptable fuel range.
Everyone was so hyped up about the 7 gallon fuel tank on the FX Nytro that there are many options available, yet stock for stock it has the same fuel range as the Apex.
One tip with the Apex is you can typically ride at least 10 miles after it first runs out of gas. The fuel pickup is at the front so if you restart it and take it easy you can coax quite a few extra miles out of it (as long as there aren't any hills to climb...).