Hi Molly, is it for a domestic dwelling, or a visitor centre etc.? The solutions will vary with the loading rate. For a domestic system it should be easy enough to get an off-the-shelf unit in a local hardware shop.
These should have an insert that lifts out. What I used to do was dig a shallow hole in the soil and put the sludge from the insert into it. Then I'd bucket out the base sludge if it was very murky, into the same hole; and then backfill. This was an area of the garden that was fenced off from gardening etc. so it was easy to just let the soil organisms get to work on the sludge and deal with it in their own time. We use ecofriendly cleaners, soaps, shampoos etc. so there was no toxic load on the garden.
If you want to avoid emptying anything, then what most people do here is plumb the grey water directly to the septic tank with no trap. Then it gets emptied annually during the septic tank desludging process (if you follow the regs...)
I looked up "domestic grease trap Vancouver" and also Victoria but didn't find anything that wasn't for restaurants. You could try your local hardware shop and show them the picture on the JFC Civils website if you wish. They may be able to help.
Also, can I ask you, what are you doing with black water - can they go in together and simply ignore the grease trap?
You could also opt for a woodchip filter for grey water (as per www.solviva.com) and leave out the trap.