Dennis, put in an F&T trap on the outlet of the heater. No check valve, no vent. That should make it work fine with a condensate tank. BTW, I happen to have a Hoffman tank and pump that had about 4 years of use. It was removed when I put in the new boiler and went to a gravity return. It works great. It's a Hoffman WC-6-20B. It has a cast iron tank. I'd take $400 obo.
They used to come with all Vacuum pumps. They are just a check valve vertically positioned, with a cap to prevent water from shooting up. Instead it would literally shower down onto the pump (if the pump was out) Did more harm than good for that application, so they are not longer shipped with the new pumps. 3/8 NPT