The vessel for kefir production does not have to meet any special requirements. What is important is that it is large enough for the planned production.
It is good to have a suitable metal lid (alternative: metal lid and band). If you have a screw cap, simply tighten it until the first resistance is felt, but do not close it completely. This way, gases can escape if necessary. In our workshop we use Mason Jar jars because they are very robust and very suitable for fermenting.