what is the easiest way to remove 40lbs of sand?
How big is your tank and how big are your fishy?
A couple of options:
Is the sand eating a new thing? - if so, it could go away once the novelty wears off...Penelope seemingly eats sand, but in reality it is a by product of scrounging for tidbits of food she missed at mealtime. I swirl the sand once a week to stir up leftover scraps, grab it with a net and let the filter capture what I miss
If it is easy to move the fish to a temporary locale for an couple of hours, you can drain the tank and use a dust pan to get some real mileage on removing the sand. Then add some water so the left over sand floats and use the the siphon like Steve mentioned.
If you can't move the fish (or the turtle) then....move them anyway. If scooping a little bit at a time stresses them out, it is prolonging the whole endeavor.
I'll cross my fingers that the sand eating is really food scrounging and that it stops soon.