Building a sink
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Create a cube. With STRETCH change its height at Z = 0.1m.
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In SUBDIVIDE mode, divide the cube into 8 x 8 small regular cubes.
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In mode MOVE, raise the cube to Z = 0.6 (you can type 0.6 in the Z box)
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Go to CURB mode, with the sub-option "both dimensions".
Click on the cube exactly in the center of the grid and lower it to Z = 0.1 (you can type 0.1 in the Z box).
And here's your sink !
If you want a bathtub you can stretch it with STRETCH.