I tried loads of things that may clear a blocked shower drain (store-bought liquids, vinegar+baking soda, running hot water through) over the past months, but the water still drains very slowly. After a minute of shower you would stand in 3-5cm of water.
When I remove the shower head and stick the tube in the drain (and turn on hot water on max strength), after like a minute or two I start to see air bubbles coming up and then after a while the water suddenly drains. Still, when I start showering again, the same old problem comes back.
Do you have any idea what could be the problem? Could it be that the blockage is somewhere further down the system (the apartment I rent is on the 4th floor)? Is it fixable by myself or need to call a professional?