So I finished installing and plumbing a secondary pump in my 21 H2O and it turned out pretty easy project.
Before:
Located and drilled the hole
Prepped the parts
Installed and sealed the thru-hull fitting
The rest was done next day to allow adhesive to cure. Connected the hose to the fitting and routed it to the bilge pump location
Installed a little starboard platform right next to the the one from the factory and mounted the pump with Ultra Safety System switch.
The rule float switch on the right is not mine, it's from the factory
Finished by running