Hi Dan
Taking the second part of your reply first , I have to say I agree that more advanced studies into certain aspects of venous return ( centrifugal effects ) in the lower limb are required than can be provided by a bottle of sauce .

With regard to the glove experiment as a means of demonstrating that stretching out veins does not make for an effective pump , I feel something that simple is really all that is required .

But let's say you take a length of vein , valves and all ,fill it with blood and tie off the bottom end . Now hold the vein upright and stretch .Yes the circumference will decrease but the length will increase giving little change in volume and a very ineffective pump .
You mentioned Bernoulli's principle ,above , but that is about the conservation of energy whilst the foot pump is all about generating energy .

The main people in the foot pump story are AMN Garder and RH Fox ( although many others have played a role before and since ) . They wrote " We have discovered a venous pump mechanism in the sole of the human foot that is able to return blood from the leg up into the abdomen with no assistance from muscular action " . And to a certain extent they had . It just that ,in my opinion , they misunderstood the mechanism by which their pump worked .

They carried out a series of experiment including introducing a contrast medium into the deep plantar veins . Toe flexing did not move the contrast medium out of the veins but weight bearing did so the pump does not work by muscular contraction alone .

How does this powerful pump work ?
In my opinion ,during weight bearing , the bony arch of the foot lowers and the plantar fascia , which is continuous between medial and lateral aspects of the foot ,is stretched . The muscles between the two elements are subject to a volume which is trying to reduce ,and this results in increased intermuscluar pressure .

This powers the foot pump . No muscle to compress means a far less effective pump . Muscle with some tone will produce a more effective pump etc