This is the best plug we've found for water ballast tanks like those found on SCAMP, as it is relatively low profile and has an easily turned T-handle.
The Garboard Drain & Plug provides drainage for bilge during haul-out. 1/2" NPT tapered thread plug provides a watertight seal with 2" diameter flange. Plug has a square T-top for manual tightening or removal. Die cast bronze construction. Installs with three #10 FH fasteners (not included).
Fasteners: #10 FH