If you make a old-style metal uniflow tank, then the amount of head in the tank is whatever the head is from the uniflow orifice to the needle valve.  To change the amount of head between upright and inverted, you have to move the tank up and down.

So far so good.

But I see two ways to make a uniflow clunk tank:  In one, you use a fixed-position rigid tube.  Then moving the orifice of the tube up and down (by twisting it from outside the tank) will change the head of the tank between upright and inverted, without having to move the whole tank up and down.  In the other, you attach the uniflow orifice to the clunk.  Then -- barring insufficiently flexible tubing -- there isn't anything you can do to change the head of the tank relative to the needle valve.  In fact, because of the flexible tubing this happens all the time, and automagically.

I gather from so many folks that advocate a clunk with uniflow in part because "you can move the uniflow up and down to tune the tank" that they're talking about a uniflow with a rigid tube.

'zat right?  Or am I confused again?

A rigid uniflow line, whose interior end can be moved but stays permanently there thru-out the flight, versus a flexible uniflow line tied to the (also flexible) pickup line, so it can't be "located" in a permanent position,  therefore can't be adjusted.  Right? 

I've used both and can't tell a lot of difference. 

There is no orifice in the uniflow line / tube.   You described 2 ways to make a uniflow tank,  both will work.  So I am not clear on what you are confused about.

Orifice = opening = end of tube.

I wanted to know if one was better than the other.

Orifice =  restriction

Not to argue or anything, but according to the dictionary:

"Definition of ORIFICE
: an opening (as a vent, mouth, or hole) through which something may pass "

No mention of restriction.  See for yourself: http://www.merriam-webster.com/dictionary/orifice

(and yes, it was probably a poor choice of wording on my part).

I like the rigid plastic tube for uniflow, seperate from the engine feed clunk.   

Thanks.