First you need DROP within the confines of how much hose you own.
With our 4" gravity dredge [
www.goldgold.com/gravitydredge] (currently not available) you should have a minimum of 4' of drop from the bottom of the upper hole going down to your sluice, NOT just from the waters surface of your upper hole. Anything less and you will lose your prime over time due to cracks/pinholes/coupler(s) leaking air into the hose.
Up's & down's as well as ANY bend in the hose will reduce suction and they add up quickly!
I didn't like the 'flat-hose-gate' as is tends to want to stay flat. We simply used a 4" plumbers plug (with the giant wing-nut) at the bottom, with the hose off the sluice-pipe inlet. (we are using an old crash-box sluice) Once all the air is out of the hose we release the plug and push the hose onto the inlet pipe. This usually allows us to leave the water running 3+ days straight and still check the box occasionally. We're thinking of going to a 4" ball valve but they aren't cheap!
We did one run near the end of our season, where we had 90+ feet of hose with a 6' drop and I swear that dredge could have suck-started a harley!!!
In our area (pretty far back into the wilderness) we usually stash the hose and sluice (minus the carpets/riffles) high enough up the bank that anglers and wardens haven't found them yet. Saves hauling everything in and out every time.
Buy your hose face to face [no shipping] and always buy in 100' length, it's cheaper!