How to properly drain petrol from the tank of a modern car

In many cases, keeping a personal fuel reserve is not paranoia at all, but a perfectly rational tactic employed by experienced drivers who are unwilling to take risks or play roulette with petrol stations. Not to mention the ever-present need to refuel small motorised equipment – garden, construction, and watercraft. Today, obtaining a can of fuel without unnecessary hassle is only really possible by siphoning petrol from your own car's tank. However, doing so is not as straightforward as it seems.

Sensible, non-commercial hoarding was traditionally a strong suit of the Soviet, and later Russian, motorist. This habit of stockpiling has paid off over the years, and sometimes even been a lifesaver. Not so long ago, our grandfathers and fathers would create garage reserves of anything they could manage not just to buy, but to 'get hold of' for their beloved cars. Garages would accumulate tyres and rims, suspension bushes and ball joints, containers of oil and antifreeze… Prices were rising visibly, far outstripping wages, and certain items regularly became scarce or vanished from shelves altogether.

Since most petrol stations today won't fill a canister directly, siphoning petrol from the tank into a can is, in some cases, necessary and unavoidable. There are formally two ways to do this. The first is through the filler neck, using a hose: either by gravity or with the help of an additional external electric pump. The second is by using the car's own fuel pump.

For the first option, you need a thin, rigid, and fuel-resistant hose. Unfortunately, no rubber hoses, even those originally intended for transferring fuel, will work for a modern car. On most vehicles, there is a convoluted labyrinth from the filler neck directly to the tank, which a thick, soft rubber hose cannot navigate. Looking into numerous accounts of siphoning fuel from modern cars shows that a rigid polyethylene tube (marked as PE) is ideal for this job. Such tubing is sold by the metre on online marketplaces and in pneumatic equipment shops; you'll need at least two metres, and preferably 2.5 to 3 metres.

A tube with an outer diameter of 6mm and an inner diameter of 4mm will fit into virtually any car, but if you're lucky, an 8mm outer diameter and 6mm inner diameter tube might also work. In either case, this kind of setup limits the siphoning rate – you won't be able to fill a 20-litre can quickly through it. Without an additional pump, i.e., by gravity alone, it will take about forty minutes or even an hour. But this is an inevitability you simply have to accept without argument.

Before starting the process, it's advisable to check the technical documentation to see what the route from the filler neck to the fuel tank looks like on your specific car. This is easy to look up online. Typically, you'll see a tangle of pipes of quite a complex shape, but in most cases, a thin, rigid hose can navigate it. It's a good idea to look at the pipework beforehand to understand where the hose might get stuck and how you need to twist it to push it further until it's submerged in the fuel, as well as where any dead ends are (for example, an air vent or a line to the charcoal canister). Incidentally, it's a good idea to lightly trim the end of the tube with a knife to smooth the edges – this will help it pass through the labyrinth more easily.

It's easy to tell if the tube has reached the fuel level – just blow into the tube periodically as you push it in. If there's no resistance to the air, keep pushing. If there is resistance and you hear gurgling, you've made it!

To start the gravity flow, you can again use your mouth, or you can arm yourself with some kind of 12-volt pump, like an aquarium pump. We once tested such a device for its ability to pump oil out of a sump through the dipstick tube, after which we flushed it with petrol – it handled both hot oil and fuel without any issues.

Moreover, this pump can be used both to start the siphoning process and to speed it up overall. With the pump, it will be at least three times faster, and the only inconvenience is that you'll have to connect its fittings to the polyethylene tube using whatever pieces of rubber hose, tubing, and clamps you have to hand, because you won't be able to fit the rigid, slippery, and completely non-elastic polyethylene tube directly onto them.

Another method of draining petrol from the tank is to use the car's own fuel pump. However, this requires some work inside the car, not just outside, which isn't something everyone can manage. Using the fuel pump, you can drain the fuel either directly from the pump's outlet fitting or by connecting to the fuel line under the bonnet – at the fuel rail or pressure regulator.

In the simplest version, you remove the rear seat cushion, open the access hatch for the fuel pump, disconnect the supply pipe, and attach a hose to the pump's outlet fitting instead. This method doesn't require the 'gastroscopy' with thin, rigid polyethylene tubes – you can use a fuel-resistant reinforced hose with an outer diameter of 10-12mm and an inner diameter of 8-10mm. With this, a 20-litre canister fills in just five to seven minutes.

The difficulty lies only in supplying power to the fuel pump – you need to find its relay in the fuse box, remove it, and insert a jumper wire between the open contacts. On some cars, you can force the pump to run via the diagnostic connector (also using a jumper wire), but in either case, you still need at least a basic knowledge of electrics. And of course, you mustn't forget about fire safety – if you're not confident in your abilities, it's better to stick with siphoning through the filler neck.