Draining gas tank questions -- Is this thing a vent? How does my tank look in general?

Hello, I am trying to drain the gas tank on my boat as it has been sitting for quite some time and the gas is likely bad. Here is a photo of the park of my tank I can see:



First, I just want to make sure I know what everything is. I labelled the main parts above.

1: I am not sure what this hose goes to, but I'm going to trace it later
2: This is my fill line
3: This goes to my engine
4: this is electrical and at least some of it goes to my sending unit
5: this is my fuel sender unit
6: I am not sure what this is

So here are my specific questions:
1) Hoes does my tank look in general? I know that it's hard to asses from a photo, but does anyone see anything that make them think "oh wow this tank is falling apart like tomorrow"

2) I have some corrosion on the fuel send unit. I kind of want to take it off and clean it, but is that a bad idea for any reason? I imagine that I can just pop it off and then back on, but I've never done this before so maybe it would need to be like calibrated or something and I want to make sure that I can just pull it right off and put it right back on before I mess with it.

3) My actual main question is... I'm trying to drain the tank. I have disconnected #3, above, the hose that goes to my engine. I tried putting just a priming bulb on there and sucking the fuel out, but the priming bulb didn't have enough strength. It felt like it locked up, like there was too much vacuum pressure inside the tank or something for a priming bulb to get the fuel out? I know people usually use pumps, but I figured that I would try a bulb first and just manually pump the fuel out so I don't have to buy a whole pump. So if my priming bulb just doesn't have
enough power to get the fuel out, I figured maybe there's a vent or something I can open that would release the vacuum. I saw #6, above... it kind of looks like it's a vent? I can't see anything else that it obviously does. Anyone know if this is a vent and if cracking it would allow me to pump the gas out? Or maybe if my fuel sender can just pop off and pop right back on, maybe I can pump it out while the sender is off? Or is there some other trick to getting fuel out without a pump?

Thanks in advance!

1. Tank looks fine.

2. Yes, you can just take it out and put it back in. It's just the float that makes your fuel gauge move. Scrub it really well and sweep up all of the debris before taking the sending unit out. The hex head screws around the edge are what holds it in place, as well as the phillips that the ground wire is attached to.

3a. My guess would be that the priming bulb is the problem. If you're trying to use it like a siphon, the receiving container needs to be lower than the one you're pulling from. That's why pumps are used. Also, the tank doesn't hold vacuum.

3b. Also best guess, but #6 in your picture was probably just an extra hose location that wasn't used, so they capped it off.

4. #1 in your picture is your fuel vent hose. It either goes to a seperate fuel vent on the side of your boat, or to a vent tube on the gas fill.

MikeSchinlaub said:

3a. My guess would be that the priming bulb is the problem. If you're trying to use it like a siphon, the receiving container needs to be lower than the one you're pulling from. That's why pumps are used. Also, the tank doesn't hold vacuum.

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I'm just trying to manually pump it. Like I have one end attached to the line that goes into the tank and the other end in a bucket, I'm just trying to pump using the bulb. When I pump, I get a little trickle but then the bulb like locks up (it feels like vacuum lock or like the bulb is backwards or something, although it's not) and nothing really comes out.

Contrast this to when I pump out of my little 5 gallon portable tank, when I squeeze the bulb, I can get a pretty steady stream of fuel going into the bucket.

Hm. I assumed there wasn't vacuum in the tank either, so I'm confused. Guess I'll keep digging... thanks....

jimmwaller said:

Contrast this to when I pump out of my little 5 gallon portable tank, when I squeeze the bulb, I can get a pretty steady stream of fuel going into the bucket.

Hm. I assumed there wasn't vacuum in the tank either, so I'm confused. Guess I'll keep digging... thanks....

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Could be I'm just dumb and don't know what I'm talking about. Stick around for a bit and see what other people think.

That big fitting coming out of the pickup on #3 is an antisiphon valve.... meaning it has a small check ball in it that prevents siphon and you need constant suction on it to pull fuel. That is why the hand primer bulb is struggling. Now that can be gunked up and restricting flow as well, it could be failed all together and stuck... it really could be any number of things. But I suspect that is causing your current issue.

Pmt133 said:

That big fitting coming out of the pickup on #3 is an antisiphon valve.... meaning it has a small check ball in it that prevents siphon and you need constant suction on it to pull fuel. That is why the hand primer bulb is struggling. Now that can be gunked up and restricting flow as well, it could be failed all together and stuck... it really could be any number of things. But I suspect that is causing your current issue.

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Oh okay, thanks, that makes sense and matches what I'm seeing. So what's the recommended course of action here, do I actually need an electric pump or is there some kind of trick?

jimmwaller said:

Oh okay, thanks, that makes sense and matches what I'm seeing. So what's the recommended course of action here, do I actually need an electric pump or is there some kind of trick?

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I have a cheap electric pump I use... you could also just pull the fitting and replace with a regular barb fitting for now to drain, or pull the sending unit and siphon from there.

For the barb... pretty sure its 1/4 NPT x 3/8. If you have a fuel water separator with threaded fittings you can probably just swap it with one of those for now even. I'd probably just pull the sending unit and drop in the hose and siphon it out. Gives you good access to inspect the inside of the tank as well.

Jimm, The aluminum tanks will develop pinholes on the bottom of the tank. It is best to drain the tank, pull it out and inspect it for corrosion.

Most boat builders stopped using aluminum tanks in the early 90's so your tank is likely pretty old. Another reason to inspect it.

If it were me, I would remove the gas gauge sender and using one of those "shake-shake" siphons, siphon the fuel thru the garboard drain (boat obviously must be on the trailer), using a piece of 1/2" copper pipe, into some Jerry cans. The 1/2" copper pipe should just fit thru the garboard drain and the plastic hose of the siphon. Put the jerry can on the ground under the drain so the fuel drains out of the copper pipe into it.

The fuel sender is easily replaceable as well, if the tank is still good.

DISCONNECT the battery cables before doing any work on or near those wires.