And another stage - again splitting things off into an evenly shaped portion. This time I split those rails by some lines in the top view.

Now the odd areas to fill are a lot smaller, now possibly sweeping to a point in those spots won't make such a mess.

But you know what, after looking at this shape I think my earlier comment about extrude + fillet was a better strategy overall.

But if you want to get a more gentle curve along the front part of the basin, what you would do is instead of doing just a straight extrude down, you could put in a few cross sections and do a loft or sweep down, that will let you control the shape and put a gentle curve in there instead of it just coming down straight. But don't try to model the bottom rounded part with the loft, have the loft come down to a flat planar bottom, then put a fillet on that bottom to give you the round. Let me know if you would like some samples of this other strategy.

I think you'll get a better result in this case if you don't try to explicitly model the rounded bottom area, but instead let a fillet (possibly with a blend shape instead of circular if you want) do that rounding for you. Does that make sense?

- Michael