Lymph Fluid, Bottom of Shaft

Hey ya’ll,
Quick question for something that is kinda new to me.
I have added low vacuum pumping to the end of my stretching/hanging routine.
I started with 60 min dynamic pumping up to 5 Hg for five minutes then 0-1 Hg for 30 sec (with a heat wrap around the tube) and repeat.
When I was done I had a section on the very bottom of the shaft that was bubbled (lymph). No fluid build up anywhere else on my shaft.
So, I cut this down to a 40 min routine and still had the same condition.

This is not an extreme routine by any means (and 5 Hg doesn’t even give me a full stretch in the tube) as I am well conditioned and way past any newbie gains.
I like the fact of the low vacuum pumping at the end of my routine as I am hoping it helps with gains from the stretching/hanging. I need something to get some gains back going.

With that said, is this just being caused by some excess skin sliding in the tube?

Thanks for any input,
Michael