Which Caulk?

[Kirk]

I am installing a new livewell pump on my boat. The instructions say to use caulk to close the opening where it fits through the transom. It went on to say
Silicon Sealant is not recommended. What is the right kind of caulk to use?

 

[minner]

3M 4200 Marine Sealant

 

[Kirk]

Thank you!