Your '86 shouldn't have an anti-siphon valve, so all ya gotta do is remove the fuel line coupler from the fuel hose and use the primer bulb to siphon it out.
If by chance there has been a anti-siphon valve installed you'll have to replace it with a straight 3/8 nipple.
The A/S valve looks just like a nipple but it has a ball&spring seat assembly built it in. When your fuel tank is situated below the powerhead, like in a bassboat, then you don't even want it on there, remove it and don't put it back on.
Pontoons and deck boats where the tank is above the engine are what a/s valves are designed for.