Is there a limit as to the length of straw through which it is possible to drink? I remember years ago seeing something in a book which said it would be impossible for someone on the upper floors of a house to suck a drink placed at round level through a straw. I've just tried it with some extra-long straws which I bought, and I couldn't do it. Is there a formula or a scientific explanation to say why, or is there a maximum height from which this can be done?

I image there is a limit but I just got a mouth full of salt water after syphoning of the aquarium and that was around four feet of tube... Blaaah

I asked (who else but?) one of the students and he said it would depend on the strength of a persons lungs. If you used a pump then the limits would be imposed by the strength of the straw which would collapse in on itself. He could not, however provide me with a formula for the length of straw.

I think it would depend on air pressure. Memories of my Physics classes in the 1960s says a pump could suck water up 30 feet.

Assumptions:
The straw is not a limiting factor, it will not collapse under any circumstances.
The lips are fixed to the straw, nothing comes between them (no sucking air).

Then your formula is:
Hmax = C/(A*d*g)

Hmax is the maximum height you can suck your liquid.
C is your individual sucking force, to be determined experimentally.
A is the cross section of your straw, the wider the straw, the harder it is.
d is the density of the liquid, usually 1 for water, oil is easier, mercury is very tough.
g is gravity.

Interestingly, I don't think it depends on air pressure, but I cooked this up myself for fun, so please review

When you suck on a straw you're creating a partial vacuum-So the liquid is pushed up through the straw by air pressure to the height where the weight of the liquid column equals the difference in pressure. Atmospheric pressure at sea level ~14.7 Lb/in^2.
Were you able to draw a perfect vacuum in your mouth you could theoretically drink from almost 34 feet up. In truth, before you got a taste of water you'd be drinking your own blood from the hemorrhaging blood vessels of your mouth.

Remember how easy it is to draw a hickey on someone's neck with just 1 lb of vacuum?