How to clean a unit-bath

Hi everyone,

It's my very first time coming to Japan and surely my very first time living in a typical 10m² apartment of Tokyo.

My apartment comes with a pretty simple, typical, Japanese prefabricated plastic(?) unit bath. Since I've noticed a kind of drain on its floor, covered by a lid, I have a question for those of you who are familiar with that.
My doubt is: after cleaning the bathroom/sanitary, since everything is so close to each other, could I just rinse it all using the shower head and let the water flow in the drain on the floor? Is that just what I am supposed to do or is it usually not recommended? Any general advice on this matter?

I've tried to look for an answer on this subreddit but I haven't found anyone talking about it, I'm sorry in case it's a repetition.

Thanks to everyone who will take some of their time to help me ✨️

by Shot_Maintenance9890