I have a plastic Tenor Recorder which I understand can be washed with soapy water.
I am concerned if the lever can also be immersed or do I have to clean it another way.
Although most of the plastic recorder can be cleaned with water and mild detergent, since the keys have pads, you want to keep the keys dry. From Yamaha's website:
Resin recorders can be washed in one piece using a neutral kitchen detergent. For instruments equipped with keys, take care to avoid allowing the keys to become wet.
My Yamaha tenor recorder is built in 3 parts; I can wash the head and middle joints easily, but I need to be careful with the foot joint, since that's the section with the keys.