Ok, you got the older model. The output adapter of that OTP is not slip, I am pretty sure it is threaded. It would not make sense to have it as a slip. If that was the case, you would need to glue the pump and that would make it impossible to remove the pump to clean and service - so I am pretty sure that is threaded.
Here is the pump you would need...
http://www.coralvue.com/reef-octopus-otp3000nw-skimmer-pump