I have tested it and works really, really good. Will bring it up next time, thinking of putting a bolt through the bottom of the nozzle at the end, so big rocks don't block it. Now to answer your question mate, looks good, this pump, but can't work out how to use the pump!! Actually just made another one, will have to do a shot soon, I designed it for Spot X for the gravel, I think it's better than my last one. Hey Yobs how are ya mate, itching to get out, but gotta move, so busy, oh I hate packing, throwing stuff out, so much stuff gone to tip. You can go as small as needed to get into the cracks. One thing to note is that we reduced the 25mm suction hose at the tip to prevent blockages by using a small nozzle cut down to 12mm. Here's a before (left) and after (right) of a bedrock area done with our original first type of ground-based setup. Note: Just added the 30cm steel ruler for scale. Still some kinks to work out with this new design. I'm still debating on whether or not to add a small base to the pump to kneel or stand on. The pump itself is a Jabsco Manual Bilge Pump and they run around $130-ish. Our previous design was all used on the ground with the pump attached to a small separate stand. It can also be left on the ground in an upright position (to let gravity do the work). Just need to attach the main PVC section to a sturdy backpack.

That's why this type of hand pump works so effectively

We are under the same rules and regulations here in N.S.W.

Instructables making hand dredge