You know, I have been following discussions about the suction guns for many years now. I see all kinds of "this and that" ways of doing them. Curves, traps, neck downs, etc.
I have never had to neck mine down....as the suction is so great it will pull up anything my crevice tools will loosen.....and as deep as I can get them.
Having used one for the past 30 some years (originally getting sand shrimp for fishing bait), I am pretty good at it. I have even given lessons to those wanting to learn. Suck and shoot and be very quick about it. Don't make your lift to high. One needs about 1-2 inches of water overlying your spot. Have some good crevice tools. My Oregon mining partner has been making all mine (crevice tools) for the past 25 years.
Enjoy and get some gold. Easiest ...cheapest...method I know...and I have been doing this for a very long time.
Bejay
Here's a very good video on building a shrimp pump. From Home Depot to completion. Once the link opens, Scroll down to "How to Make a Ghost Shrimp Pump (Yabby Pump)" 19:57
shrimp pump - Ask.com YouTube Search
Reed. I love your setup. Only thing missing is a cold one on the cup holder and the rest of the 6 cooling in the creek. No wait, two cold ones as you have to keep your helper hydrated. ;-)
6 inch high "meat lug". Buy one and never have to buy another. When 1st placing in water (and empty) one can place a foot inside to hold it from drifting down current. Plus the "meat lug" fits a quad rack like a glove. And they stack, leaving a space between them for your crevice tools, gloves, etc
They make a 10 inch high one and a 6 inch high. I have both.
Bejay
wow! the price for this is cheaper than for a mortor mixing tub from Home Depot and more durable.