1. Open or reset your 3dsmax. Draw a line in Front viewport (look at image below for reference). Activate 3D snap toggle to let you easily draw line with precision. Make sure you draw in grid point. Also start point and end point should be in the same X coordinate. Right click to finish creating line.
2. Go to Modify tab. Activate Vertex selection. Select all points except several vertices at left side. Right click at selected vertices and choose Smooth. You will have curved spline like image below.
3. De-activate all sub-object selection. In Command Panel click Hierachy tab. Click Affect Pivot Only button. Then, move Pivot Point to exactly at left side of line. Use 3D snap toggle to move Pivot Point precisely at grid point. When finished, click Affect Pivot Only button again to turn it off.

4. First, activate Perspective viewport (just right click in Perspective viewport). In main menu, click Tool>Array. Array window willl be opened. Activate Rotate Total button (small ">" button). Enter 360 in Z. . Use Copy, so you can modify cloned object later. And Enter 4 in Count. Click OK. You will get 4 spline like image below.
5. In Top viewport, select one of the left most spline. And delete it. By deleting it you have half of object. Next, you will focus on creating half of washbasin object.
6. In Front viewport, select one of spline. Go to Vertex slection and move several vertices like image below. Then, in Left viewport also modify vertices so you have profile like middle image below.
7. De-activate all sub-object selection. Using Select and Rotate Tool, in Top viewport rotate spline while holding Shift to clone spline. For cloning method use Copy. This option will enable us to modify cloned spline..
8. Make sure cloned spline is selected. Activate Vertex selection. Select several vertices. In toolbar, activate Local for Reference coordinate system. Then modify vertices position. Always modify vertices, with activated Local coordinate system, so you don't ruin spline shape.
9. Repeat above process by cloning other line and modify its vertices. This could be a long process. And you have to modify each vertex carefully. Tweaking vertices is not an enjoyable job. But, trust me, the hardest part in Surface Modeling is here. The rest is not.
10. Finally you have something like image below. How many spline you used to form the "cage" is up to you, the more you use the more detail you may have, but more time you need to tweak verices position. Use less spline possible is wise decision. I suggest you save your work before continue with the next lesson. You can download 3dsmax file containing these splines.
11. De-activate all sub-object selection. Select one line (for example no 1). In Modify tab, go to Geometry rollout, click Attach button. Then ,click all spline in sequence(from 2-10). Attach will combine all spline into one object. When finished, click again Attach button to turn it off..
12. Next, we are going to create a spline "cage". Notice, that right now we have only vertical spline, we need to connect all vertices using horizontal spline. That's why we use CrossSection modifier. Make sure your spline object is selected. In Modifier List, choose CrossSection modifier to apply this modifier to object. In Parameters rollout, use Smooth..
13. Next, "skin" the cage. Apply Surface Modifer to cover the cage with surface or skin..
14. Last step, apply Symmetry Modifier, with Axis=Z and Flip activated. You have your own washbasin model. The quality of your model is depending how well you tweak the vertices position in earlier step. If you wish to edit model, I suggest you open your 3dsmax saved file earlier.