Possibility Number 1:
Insert the seal correctly on the vessel. If it is not placed with the nose in the groove of the vessel, the 7-way-valve does not close properly and there is a higher distance between 7-way-valve and vessel.
The partition in the area of sand and pure water chamber is not correctly inserted in the sieve bottom. Then the 7-way-valve is also too high.
Make sure that the seal at the top of the vessel is in a clean and flawless condition and that there is no sand on it.
You can cover the O-ring with Vaseline, which is used to preserve the O-ring and additionally supports the sealing.
Possibility Number 2:
Your vessel is leaking, have you fitted the 7-way-valve correctly with the notch on the underside of the lid and the notch on the filter?
It is best to add the 7-way-valve to the filter vessel with the help of a second person.
Press the lid onto the filter vessel, making sure that the lid closes with the vessel.