Perhaps you can design an extension of your home for a fourth bedroom. Of course, you'd have to talk to an architect and someone who knows a lot about drainage. If you block or clog the drain when building or pouring the floor with concrete, it could cause your home to begin to collapse. Drainage protects your home from going underground, you know. The water must have somewhere to go. When my neighbor poured concrete under his kitchen, everything became clogged, and he had to call in specialists from drain cleaning in Toronto. He was very upset about his mistake. So be prescient and don't make these mistakes.

Painting them black (if the colour of your door handles and lights are black) would be quite a nice feature, unless you want to hide them. That would be a nice touch to complete the look, making it look modern and keeping a coherence in the design.

Its acrylic do in theory an overflow could be drilled through and fitted, but the plumber might not want to do this as if it goes wrong he'd be liable, but if you give him a guarantee in writing against a mistake on his part he might.

I have a double sink the waste pipe runs into the washing machine drain pipe. I cleaned the pipe after having a repair to my washing machine. Since then I have bubbles coming up the drain pipe when I empty my sink. If I fill my sink with just water it drains no problem if I have used washing up liquid the bubble come up and out of the pipe causing damage to my units.