Coleman also offers a similar collapsible 5 gallon "Water Cube", (which we use for spare water carrying capacity when at Joshua Tree N.P.) but I would vote against using it as an inside grey water tank for several reasons:
... Even 10 liters will get a bit heavy trying to disconnect it and lug it out from under a sink without spilling.
2. Spillage.... As above, as soon as you touch one of these the water will head for the open port and be all over the inside of your RV
3. Capacity.... 10 liters will fill fast and imagine the mess when the container is full and there is still a inch of water in the sink.
4. Damage.... You can't really just squeeze these to fit into available space. Any edge or corner contact will become a wall failure point from rubbing, especially if you forget to or can't empty it and have to drive with it in place.
5. Venting... The real biggie. The sink can't drain into a closed container unless there is a way for air to escape
. This means adding some sort of a vent, see #1, #2, & #3.
I would still opt for a closed circuit, outside tank, that could be brought inside as necessary.