I plan to add a bath in my basement. However, there is not a rough in. The house's plumbing is connected to a septic system. The pipe going out to the septic is located about halfway up the basement wall.

The plumbing from the upstairs is exposed, as the basement is not finished. However, I don't see any way to tap into the vent from the basement.

I have a macerating toilet to install and I will be hooking the sink and tup to it to pump the wast out, but I'm stumped as to the vent.

Tap the vent into a drain line but not a fixture line that does not have a toilet on it. The drain line will be a wet vent. The fixture line will not be vented until it hits the drain line. Put the wye in line turning up so the upper drain will not flow down the vent.