Filling up with fuel in Russia (especially Eastern Russia) and Mongolia is not up to the standard we have at home. On at least three occassions we had fuel overflowing on the ground because we could not shut off the pump. Many pumps do shut off but some don't and unfortunately you never know which one is not going to work. After a few fills you can pretty much gauge how much fuel to buy based on the distance travelled. My advice is to buy slightly less than you need. This means that you might not be able to fill your tank to capacity but at least you won't have to worry about getting fuel all over your bike. Also, make sure you place the hose in the tank before you go and pay for fuel, otherwise if the lady behind the counter hits the button too soon or if you press the button on the side of the pump too soon fuel will go everywhere. This happened to our friend who was travelling on a motorbike. He had unclipped the hose from the fuel pump and had it pointed in the direction of the bike when the lady behind the counter hit the on button and fuel sprayed all over the bike.
Part of the fun of travelling is to experience new things. Ordering, paying and filling up with fuel in Russia is certainly an unforgettable experience.
Talking about experiences, I remember one day we were filling up with fuel and a car drove off with the nozzle still in car. The hose ripped staight off the fuel bowser. Needless to say the driver was embarrassed and the shop owner was not impressed!