How tip tanks work
The tip tanks mod is quite simple. The tip tank is connected to the wing’s main tank via an electric fuel pump. The fuel pumps are usually placed in the wing roots, one for each wing.
The pumps are then manually operated using switches placed in the cockpit. The switches placement may vary from plane to plane, basing on the available space in the instruments panel.
Once activated, the fuel pump starts moving the fuel from the tip tank to the main tank. The green light over the switch illuminates to indicate the pump is working properly.
The fuel does not move for gravity from the tip to the main. If you do not move the fuel from the tip to the main tank, you’ll not be able to feed the engine properly once the main tank is empty.
Before flight: check the weight
The tip tanks mod allow for a Gross Weight Increase STC. That means that a V35B fitted with the tip tanks is allowed to takeoff at 3600 pounds instead of 3400.
By the way, the extra weight you put in the aircraft should only be fuel. That means that you should not leave the tip tanks empty and load the extra 200lbs as passengers or baggage.
So, before flight you must be sure that the possible extra weight is all given by the fuel in the tip tanks.
During flight: check for proper operation
You want to make sure that you can transfer the fuel from the tips to the mains, especially during long flights.
If you engage the fuel pumps over a full wing tank, the exceeding fuel will pour out of the main tank trough the vents. So, you should check that the electric pumps are working properly only when the wing tanks are not completely full.
It takes an hour to transfer the fuel from the tip tank to the main tank so, once in cruise, let the main tanks go down to 3/4, then engage the pumps to refill. If they’re filling properly in almost 15 minutes, it means that everything is ok. At that point you can continue your flight.
If the tanks are not filling properly or it takes too long to refill, get back and check what’s wrong.