Welcome to the forum.
Always follow ABYC and the manufacturer's instructions. Attempt to duplicate the OEM installation.
FWIW, the OEM macerator overboard discharge on my 2000 380DA uses a seacock one size larger than required w/ a bronze reducer bushing at the seacock.
The factory installed a switch w/ bracket to ensure the discharge pump is disabled unless the seacock handle is in the open position. My practice is to close the seacock and remove the handle, except when in use to comply w/ the disabled lockout requirements.
The Dometic holding tanks are super slippery and possibly impossible for gluing onto w/ other parts. Hopefully yours already has the required additional hole.
https://cdn11.bigcommerce.com/s-g7o41rcupc/product_images/uploaded_images/vacuflush-system.jpg
A discharge pump has two Joker valves, the head pump has four.
https://www.dometic.com/en-us/outdoor/hygiene-and-sanitation/sanitation/boat-pumps/t-series-waste-discharge-pump-12v-dc-33614
Ensure the plumbing and wiring is all secure, proper and per ABYC. Follow OEM as much as possible.
Note when drilling through the hull, my preference is to scoop out inner coring and fill w/ thickened epoxy. I also line the hole bore w/ thickened epoxy so the sealant is not the sole protection for water intrusion into the inner hull.
