I installed an Echotec Watermaker on our Santorin and used the Sea Water inlet of the aft toilet, just installed a T at the seacock. I also installed a magnetic booster pump next to the seacock and led the hose into the engine room where I installed the watermaker using the hole that is also used for the radar cable, very simple and effective.
There was no need for an additional through hull, also not for the seawater outlet, here I installed a T-piece into the hoise after the manual bilge pump for the saltwater outlet.
If you want I can send you pictures or can try to upload some…
SN 120, KALI MERA, Dominica