Squeeze an enclosed fluid and the pressure it feels is the same everywhere. A small force on a small piston makes that pressure; a large piston turns the same pressure back into a large force. The catch is honest bookkeeping — the big piston barely moves, so the work you put in equals the work you get out.
Every layer of fluid has to hold up all the fluid above it, so pressure climbs steadily as you descend: P = P₀ + ρgh. Only the depth h and the density ρ matter — a narrow straw and a vast lake reach the same pressure at the same depth. Change the liquid, lower the probe, and read the gauge.
A submerged body feels an upward push equal to the weight of the fluid it displaces: F_B = ρfluid Vsub g. Float when your average density sits below the fluid's, sinking only until the displaced fluid weighs as much as you. Dial the block's density and swap the liquid to see where it settles.