water level min tube diameter

I plan on using a water level to set the guttering fall. I was going to use clear tubing and was wondering what minimum diameter of tubing should I use and what length is manageable?

12mm bore is a good reliable size. If you get too small the skin tension on the surface of the water can mess up the levels.
I've used 16 metres at times

Yep. Wot Bob said. If you look closely, you'll see that the water creeps up the wall where it touches the tube to form a curve. (aka the meniscus) With a 1/2" tube you'll get a good flat area in the middle, which is what you use to take the reading.

The good thing about water levels is they can be as long as you need to do the job and still be perfectly usable. They can be ungainly if you're using a 20m length to measure points only a few metres apart though. :U

Remember you only need the clear polythene at each end to be able to see and mark the levels.

For years I have used two lengths of about 200mm x 19mm (you could use 16mm or 12mm - not smaller) to which I have fitted a snap-on O-ring hose fitting (I used a 1/2" sprinkler adapter fitting and clamped it onto the threaded end with an irrigation clamp - there is little water pressure. You could use an end joiner fitting).

This means that all you need to do is to attach one to each end of any hose fitting used on most standard 12mm garden hoses - giving you anywhere from 20-30 metres or more by simply joining hoses together. I have a 10m length that I find useful and carry with me to jobs.

Easy to use and compact and mostly you can get access to a hose without having to carry one with you.

Thx Bloss,

But alas, I've already shelled out for 12 metres of clear 12mm tubing (not cheap!!). The garden hose idea did cross my mind and in the future when I need greater lengths I'll make up some of your adaptors. Thanks again.

Is there a quick way to remove all the air bubbles? I filled the tube from the garden hose and it took a while to release all the bubbles. Is it best to fill the tube by siphoning water from a bucket?

I've always just connected it to a tap, and run it until the stream is clean, 30 seconds at most.