The DOD Rubberneck has got a TRS input that can be used to conjoin a three function foot switch.
By this you can control the tap function, the rubbernecking and also the modulation.
By connecting tip and ring to the ground you can produce an external tap signal.
If you want to use a multi tap tempo pedal (like the Disaster Area SMARTClock or the Selah Effects Quartz Timer) to synchronize the Rubberneck with a midi clock or other pedals you will have to generate such a connection as mentioned above.
If you already use a DigiTech FS3X triple momentary footswitch to control your DOD Rubberneck it would be easiest to modify your device.
For this you will have to connect the tap tempo with an additional installed 1/4″ TS jack (signal to tip and ground to ground).
For this modification you only need a drill, a 1/4″ TS jack, 2 pieces of flex and solder.
By using a TS/TS cable you will be able to link an external tap pedal to the new output.
If you want to save space and don’t have an FS3X pedal you can also produce an adapter cable for the DOD Rubberneck.
For this you need a 1/4″ TS plug and a cable in the desired length.
You will have to connect ground to ground. Tip and ring of the TRS plug will have to be linked to the tip of the TS plug.
Now you can use the expression output of the DOD Rubberneck to connect the TRS plug with the DOD Rubberneck and the TS plug for a connection to an external tap pedal.
Tip and ring will stay constantly connected to the tip of the TS plug. When pressing the external footswitch (or the SMARTClock/Quartz Timer) the tip will be linked to ground and the tap signal will be send.