You can use silicone tubing used for airline in aquariums. Cut a small piece of natural sponge and place it on the end under the substrate (prevents clogging). You can put a small valve at the end that is outside the tank (make sure this end is below the tank bottom) and you'll only have to suck on the tubing once. When you drain off enough water, close the valve and the siphon will hold. Next time you need to drain, just open the valve.