When assembling thru-hull hardware it it not necessary to use any additional adhesives, sealants, tapes or pipe dope. The connections used below the waterline are NPT threaded connections, which when combined with the low pressures that are seen in ballast systems, make fully sealed connections that will not leak.
If it gives you piece of mind to use mechanical sealant for a belt and suspenders approach, go right away, but it's not necessary.
If you are using NPS components with straight threads, then you will need to use a sealant of some form to ensure you have watertight connections.
If you have additional questions, please contact a product expert.