Thru hull Serviceable?

[D&M]

Hi,
Reading the survey report on my new to me purchase. I see the through hulls have screws on top. Are they designed to be serviceable/serviced? (Out of water of course.) I have not arrived at the boat yet so don't know what is in the manual. Please see picture attached.
Thanks in advance for any input.
Regards,

David

[russp]

Hi David, see https://www.forespar.com/valveMaintenance.shtml

Jpg of this information attached.

Regards

[D&M]

Thanks for the information. No need to ask if they are still manufactured . I am wondering if people do replace these as they wear out with the original equipment or whether they go for a bronze or thru-hull type unit?
Cheers,

David

[russp]

Personally I wouldn't put a bronze one in. I am not aware of Marelon failures, but know plenty of sailors who were pulling their boats between scheduled lift outs because they found corroded bronze valves that wouldn't let them sleep at night.

Regards