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Yes, it has to be sealed or the pressure won’t work. I use the Rubbermaid Brilliance container which seals airtight.

Old thread, but valuable one!! I'm one whose tank barely makes it through 8 hours of sleep; on weekends, I wake up to that awful burning smell.

My husband made me an external tank, just like the one shown earlier, but we're having trouble with it. Whatever level I get it to, it does not continue to fill during the night.

The critical thing seems to be that the incoming tube into the machine needs to be well below the max fill line - and given the thing's design, that's tough to do - we might manage to place one a millimeter or two lower.

Once you fill the external container, its level will equalize with the machine's - as long as its lower tube outlet is no lower than the machine's lower tube inlet.

But it too needs to be below the max fill line on the machine. And the water level somehow needs to be somehow between the outlet tube, and the max fill line.

If we call the two tubes U and L, and the ends on the machine's built-in reservoir are UM and LM, and the ends on the Rubbermaid are UR and LR, and the max fill line is MX, then LM <= LR, LR <= MX, and water level must be = MX. That blasted tank is so shallow though, that there's basically no wiggle room.

Hopefully that makes sense - I tried to draw a diagram but, well, I have no talent and it did not go well The original photo is better than I could produce.

The only thing, offhand, that we did "wrong" is my husband got a 1 quart versus 1 gal container. That might make a tiny difference, in that the minuscule depth of water between LR and MX might be enough to feed a bit more into the machine. What DOES work well is that it's easier to open and fill the Rubbermaid than to wrestle that reservoir out of the CPAP.

Any suggestions? Please???

Can you share a picture of your setup? In my mind it’s pretty simple - the two upper ones need to be high up / outside the possibility of getting wet (to allow airflow / equalization).

The lower ones need to be as low as possible.

Looks pretty much like the photo from years back, though we have more tubing length (easier to place the external tank on the nightstand). That's easily fixed, though. And yeah, the lower ones (especially the one on the machine's tank) needs to be low - though the tank design makes it quite tough to make it much lower.

Sorry for the delay.

You need to redo it and maximize the distance between the upper and lower hoses within each container.

It looks like your hoses are too close to each other in the rubbermaid container which really limits how effective this is.