Draining Gas Tank....Safely

[TD_Maker]

Hello to all. I am in the process of rebuilding a McKee Craft boat. The boat sat for a few years, so I needed to remove the varnish-smelling fuel from the tanks. I kept reading about the different ways of removing fuel from built-in tanks, and it seems like everyone has a horror story to tell. I heard about NOT USING the little pumps you hook to an electric drill for obvious reasons, and I also read about using 12 Volt Automobile fuel pumps to move some fuel safely. I looked seriously into this possibility; however, by the time I purchased the cheap fuel pump, the fittings, the hoses etc... I was going to be into the project for at leat $70 bucks for a one time use type of thing.

Here is what I ended up doing, and it worked out great for me. I pulled off the vent pipe hose to my tanks and hooked up my air-compressor (end to end) and sealed it with tape. I turned down the pressure valve to the compressor, and started it up from scratch (empty tank) As the compressor pumped air, it forced the fuel out of the disconnected (cut the end off) fuel line for the outboard. I pumped 20 Gallons of disgusting fuel (and water) very quickly and safely. In fact, this technique removed all sorts of crap out of the tanks at the same time. Since fuel was flowing out of the tank, the tank never really became pressurized. I set my compressor at 15 lbs and it never caught up and shut down. My aluminum tank held steady.

I know I will get some people saying that this was dangerous for my tanks....I guess anything can be dangerous. However, this technique worked for me.....and it was cheap.

 

[generator12]

Re: Draining Gas Tank....Safely

Sounds to me like a good approach.

Using pumps involves "inducing" the liquid flow (negative pressure) - and there are the obvious dangers with that. What you did was "force" the flow (positive pressure) and, as long as your discharge pipe is close enough to the bottom of the tank, it should be effective.

 

[roscoe]

Re: Draining Gas Tank....Safely

I don't see anything wrong with the way you did it.

But if you have the time, you can just disconnect the fuel line from the motor end, lower it down to ground level, use the primer bulb to get it started, and let it slowly syphon out into a bucket.

It would take a terribly long time to siphon 20 gallons though.

 

[smokeonthewater]

Re: Draining Gas Tank....Safely

most built in tanks have anti siphon valves.....

 

[Home Cookin']

Re: Draining Gas Tank....Safely

good technique with the pressure.

good point about anti-syphon vavle. Easy to temporarily replace with a plain one, and use the fuel pick-up since it goes to the bottom.

one trick is to run the fuel drain hose out the bilge drain hole so you can catch it in a bucket on the ground level.

clean it with carb cleaner, swish it around, swab it out.

 

[Webbcraft79]

Re: Draining Gas Tank....Safely

Probably not too dangerous for your tanks at 15# but compressed air moving through a hose does create static. Not a good thing around fuel vapors.

 

[roscoe]

Re: Draining Gas Tank....Safely

most built in tanks have anti siphon valves.....

They Should have them.

But my cheap ars old boat did not. But it did take about 5 hours to dribble out 5 gallons.

 

[H20Rat]

Re: Draining Gas Tank....Safely

Probably not too dangerous for your tanks at 15# but compressed air moving through a hose does create static. Not a good thing around fuel vapors.

except without an air dryer on the compressor, the air was most likely far too humid for static to be a concern.

I'd be worried about 15 PSI though. That is a HUGE amount of pressure if the hose were to plug. The max I'd ever go is maybe 5 psi.

 

[TD_Maker]

Re: Draining Gas Tank....Safely

Yeah, I thought about the clogged hose thing too. However, I was standing at the exit end of the hose monitoring to make sure the fuel flow was unobstructed. Like I stated originally, my compressor was set for 15lbs, but it never caught up to actually create 15 lbs inside the tank because the gas was really flowing strong. I read another thread (on this site) where the guy used 80lbs of pressure to evacuate his tanks. Now, I would worry about that!

My feeling was that if I started with an empty compressor tank and let the compressor motor build up the pressure slowly, then it would be much safer since there was a pressure release at the other end of the hose where the fuel came out.

Hey, I may have lucked out and not blown myself up, but this method worked for me....and quickly.

 

[tomhath]

Re: Draining Gas Tank....Safely

I do something similar when changing the oil in an outboard's lower unit. Use a blow gun and direct it at the vent hole without closing off the hole, you want just a couple of PSI pushing the oil out the lower hole but not so much you blow out the seals. I suppose you could use a pressure regulator on the air line that's intended for HVLP sprayers to get lower pressure, but blowing air into the hole from an inch away works for me.

 

[smokeonthewater]

Re: Draining Gas Tank....Safely

FWIW I once modified a 1/8" wall steel bed mounted fuel tank for my truck by notching corners for wheel wells and welding in patches.... I pressure tested it for leaks afterward and 3.5 psi actually damaged the tank deforming the walls and tearing them away from the internal baffles..... 15 worked for you in this case because you never hit 15 but in the future I'd suggest that you knock that down to 1.5 to be safe

 

[kmagnuss]

Re: Draining Gas Tank....Safely

Great tip! I'm going to try it this weekend.

 

[H20Rat]

Re: Draining Gas Tank....Safely

just a interesting piece of info, but lets say the tank is a typical 26 gallon tank. If it were to build to 15 psi, the largest side of the tank would have over 6000 pounds of pressure pushing on the welds trying to rip it apart! That is the scary part about air pressure... pressure times surface area ends up in a really large number quickly.

 

[smokeonthewater]

Re: Draining Gas Tank....Safely

Great tip! I'm going to try it this weekend.

This is actually not a great idea as while it may work out there is a very real risk of catastrophic failure. Possibly serious health risk as well.... there are far better ways to drain a tank.... My choice is an electric pump but siphoning works very well and is MUCH safer.

I'm not at all trying to attack the O/P but I can see someone having a really bad day.

 

[kmagnuss]

Re: Draining Gas Tank....Safely

Well I used a similar method this weekend... used the exhaust from my shop vac aimed over my fuel filler (not covering it).
It worked, but I heard the tank oilcan a couple times. The real good news is I'm pretty sure my fuel tank is leaking. Now I've only owned the boat for a few months and never had more than 10 gallons of gas in it... and this weekend I filled it up... all 32 gallons worth. And it's definitely leaking. SO I can't say for certain if this did it or not... The REAL good news is my fuel tank is in the bow and I'm pretty sure I have to take the cap off the boat to get to it. Fun.

 

[Chris1956]

Re: Draining Gas Tank....Safely

Remove the fuel gauge sender and stick one of those "shake-shake" siphon hoses into the tank. Run the siphon hose thru the garboard drain (a 1/2" piece of copper pipe will couple with the siphon and fit thru the drain). A coule of shakes and the siphon starts. it can empty a 12 gal tank in about 5 minutes. You can also "vacuum" up dirt with the siphon hose.