New Plastimo water tank. Breather pipe?

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NPMR

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I have just had delivered a triangular flexible Plastimo water tank.

Unlike the (leaky) old tank, it only has two 'holes' in it (and no 'instructions'). The limited pictures imply that the bigger pipe is to fill the tank (logical) and the smaller, near the base of the tank to go to the water pump/outlet.

Does this system need a breather pipe or how does it manage without one? - we have one on the current tank? I was thinking that filling the thing would be problematic without one?

And another point, as the outlet to the pump is on top of the tank, how does it scoop up the water when it begins to get low? Or doesn't it?
 
No breather needed, the tank deflates as the water is used. You should arrange the tank so that the outlet (smaller) is on the bottom and at the lowest point then you should be able to get most of the water out. Also a good idea to apply a smear of silicone grease to the o-ring seals and do not over-tighten them. Make sure you pad anything under the tank (hose clips etc) that could chafe its way through the skin. I think these are a good idea as they last well (10 yrs), but are not too expensive/difficult to replace if required. Contrast with a rigid tank wedged under the cockpit which may require the engine out to get at it!
 
They stay on top. The older Plastimo flexible tanks had the large filler at the top and the small outlet underneath. The inevitable would happen and the outlet connection would very slowly drip. About 2 years ago they changed the design to have both on top - though some chandlers still have old stock. Despite being on the top, the outlet will get 95% of the water out. Use a bit of vaseline on the O ring (or even water) and as said earlier don't over tighten. I removed the old Plastimo tanks on our HT a year ago. One failed after 16 years and so both were changed. All for £100. So they last well!
 
All that has been said applies to "pillow tanks" ie ones that can collapse to being perfectly flat when empty. This of course applies to tiangular tanks.
Flexible tanks that are "shaped" ie have sides as well as top and bottom are intended to more or less retain their shape when empty and should have a vent just like a rigid tank. Using them without a vent is likely to shorten their lives.

The filler cap will have to be more or less air tight with a pillow tank to avoid air ingress.

I have a small double skinned pillow tank, made at least 25 years ago, and it is still in use!
 
With Plastimo's agreement, my tanks have only one connection. As long as the fill point is sealed (or shut off), you can draw from the same connection that you use to fill. One advantage is that there is no air (/water/diesel/ whatever else may be swillling along the deck) ingress.
 
The fun part is during the fill process, my learnt experience is not to kneel be the filler port. When the water level goes above the filler inlet on the bag the bag will burp jug fulls back at you.

I think you can spot flexible bag owners around a harbour by soaking jeans from the knee down.
 
Depends. I wouldn't try and fit a larger liner in the outer cover for a slightly smaller one as the liner will crease as it fills. If you bought the new tank complete with outer cover you should be OK, but don't overfill a flexible tank. Lots of people just fill until the filler pipe overflows but this puts a head of water on the tank and it's connections. Better to monitor the tank as it fills and stop while it is still a bit 'spongey'.
 
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