One thing you might try as a general modeling technique is instead of building each individual surface to its final edges from the start, try building pieces that are somewhat more extended and then cut them back to make the final result.

Like for example here you've modeled the basin surfaces so that the hole in the bottom is part of the surface directly (and same with all the other surfaces). Instead you might try having the basin pieces be kind of extended and then produce the hole by booleaning away a circle drawn in the top view that cuts a circular hole through there.

Carving pieces to common cutting objects like that can be a bit easier to ensure that you get matching pieces..

- Michael