party_pants said:

Bubblecar said:

Cymek said:

Do you have an outside drain you can try, near the bathroom perhaps

The outside drain is unfortunately far from the bathroom, which is more or less in the middle of the house.

To attack the problem from the drain end, I’d need a plumber with a very long mechanised snake.

See how the crystals go this time. If not call the agent and just tell them to organise a plumber. It is their job to arrange, and the owner’s responsibilty to pay for it. Don’t feel bad about asking.

Without the right equipment, you’ll have no idea where the blockage is. The plumber has the equipment.