Have you been on your knees and looked underneath.
Swift weren't very user friendly back then.
My first Kontiki 640 was 1999 and that was an arm stretch to reach.
Easy enough to extend to the side skirt.
The sink, the basin, and the shower will all drain into the same (grey water) tank. Usually this will have a pipe leaving it and going to one of the sides of the vehicle, and some form of valve to operate to allow you to control draining it. I’ve never seen on drained via a hose. Normally they are a much larger pipe, or hose.
Is the hose the only pipe that you can see leaving the tank at a low level?