ᐅ Is it possible to install a sink in a bathroom after the initial construction?

Knöpfchen schrieb:

Toilet removed.
Pre-wall installation with wall-hung toilet.
I think that gives you a better starting point / options.

But the drain pipe is vertical in the floor. We don’t want to break up anything.

Without a basement and without any work, it will probably be difficult.

I would suggest a wall-hung installation similar to this, but with the new toilet rotated 45° into the corner and then mirrored:

Then everything can be concealed within the wall system. If you build it up high with a recessed cabinet, there’s space in the upper section for towels and more. Cover the wall with the washbasin entirely with mirrors to create a sense of more space — the toilet is positioned in the corner so you don’t see yourself in the mirror while using it. Add bright lighting or install a fake window with lighting on one side. Use large-format tiles or a resin floor and wall finish, and the whole bathroom suddenly has that “wow” factor.

How deep is the room? Where is the door located, how wide is it, and does it open inward or outward?

Scout schrieb:

I would suggest a drywall installation similar to this, but with the new toilet positioned at a 45° angle in the corner and then mirrored:

Then everything is hidden within the drywall frame; if you extend it high enough with built-in cabinets, you can also store towels and such in the upper section. Cover the wall behind the basin entirely with mirrors to make the space appear larger—the toilet is placed around the corner, so you don’t see yourself in the mirror while using it ;o) Add bright lighting or even a fake window with lighting on one side. Use large-format tiles or resin flooring on the floor and walls, and suddenly the entire bathroom has that “wow” effect.

How deep is the room, where is the door, how wide is it, and does it open inward or outward?

That looks great—no doubt about it. But in our case, the tiles and floor need to stay as they are. The question is whether it’s possible to divert water from the cistern inlet to a small washbasin and then route the wastewater back to the toilet drain or directly into the cistern. This is a (cheaply) rented property; the rental period might end after 2 years, and we can’t expect anything from the landlord’s side.

Heidi1965 schrieb:

That looks great – no question. But in our case, the tiles and floor should remain. The only question is whether it’s possible to divert water from the cistern inlet to a small washbasin and somehow route the wastewater back to the toilet drain or directly into the cistern again. This is a (cheaply) rented property; the rental period might end in just 2 years, and nothing can be expected from the landlord.

In short: Nothing comes from nothing; without modifications, it won’t work.
Also, you need to clarify this with the landlord anyway, otherwise you’ll run into trouble at handover at the latest.
Your idea won’t be feasible without making some changes.

There are toilets with mini hand basins integrated into or mounted on the cistern (sometimes even using the handwashing water for flushing). However, I’m not sure how reliable they are, as I don’t think they are commonly installed.

Ecosia returns a few results for this, using terms like "toilet with integrated hand basin."