I carry tubing for:
1) water procurement/ as a straw
2) as an emergency replacment for my hydration system

I carry SURGICAL tubing for:
1) the sling elastic for an emergency catapult (slingshot?)
2) it can be used to make a very nice lashing
3) i've fixed elastic cord onto various items (tent guy lines, a few lanyards...) as shock absorbers. the tubing can replace them if necassary.
4) if i am REALLY desperate, a tourniquet.

Let me just clear up that i carry the elastic/rubber surgical tubing. there MANY other kinds, (big small, thin, thick, rubber, plastic). maybe we are talking about different kinds of tubing?

I carry the rubber tubing for the alternative/emergency uses. if you simply want tubing for water-related purposes, perhaps a non-elastic, less-bulky tubing would suit your needs better.

No, your right. You hit the nail on the head. They are all the reasons why I want surgical tubing.
Thanks for all the replys everyone, very helpful.

Right- I do use the tubing only for water retrieval.. mostly for setting up siphons to fill containers from a stream or spring that may be no more than a trickle. For that use, the longer the better- sometimes there's not much slope, and the lower down the container is below the mouth of the tube, the faster it fills.

Also, though I tried the new, more flexible typpe of aquarium tubing and it does work and packs a little smaller, I found that it was more difficult to anchor the top end in the trickle- I usually just put a small rock on top of it to hold it down into the water stream, but with the flexible tubing, the rock pinches the tubing closed. A minor thing, but annoying.

try get a short, rigid plastic tube/straw that sits inside the tubing. you can then anchor the tubing with a rock/weight without compressing the pipe.
BTW, the surgical tubing can be anchored without compressing the tubing. I think that it's just quite thick.

Another great reason to carry a paper-clip. makes a great U shaped anchor for tubing in a stream bed.