The T8.5, if so equiped, will have a shaped holding tank located below the v-berth, and you would be able to see this by removing the access panel on the top of the v-berth, underneath the cushions. If you do not find one, then look in the anchor locker for the manufacturer's pumpout fitting.
The marine head unit sits on the raised floor section in front of the port side hanging locker across from the sink. There should be a single thru-hull low and forward on the port side in the v-berth cavity for the raw water intake for the flush. If there was a macerator, it would have a thru-hull for the out flow and wiring to support the electric motor. All of these would be below the waterline.
On the original install, the toilet out-hose went to a fitting on the top of the tank, and a hose went from a fitting on the bottom front of the tank to the pump out fitting in the anchor locker. Additionally there would be a single small vent fitting high out of the water and near the bow as a holding tank vent.
Tommays is correct that all a dedicated holding tank will give you is the ability to go longer between pumpouts. I also know of people who have your arrangement with a fixed pumpout fitting. In my juristiction a macerator and over the side pumping is illegal and thus not an option. Thus if you want to be able to stay out as a couple for several days on the hook exploring your local sail area then a larger holding tank is a necessity. It certainly proved so for us.
As the 1981 T8.5 we purchased had a broken head, and the tank and hoses had over the years become permeated, we replaced the lot with new, a larger tank, and a second tank vent to reduce odors by allowing air to get into the tank more readily. This eliminated the head smell in the boat and was money well spent.
An alternative to a hard tank for black water is a holding bladder. This requires no vent hose as it expands and contracts as the volume of the contents waxes and wanes. It is not a recommended option (although I know of at least one boat that uses it) because the rolling action of a boat under sail causes the bladder to move; leading to chaffe and the unpleasant result you would expect.