Removing Aftermarket Trailer Brake Unit

[72bbblu]

The PO installed an under-dash mounted trailer brake assembly which I want to remove. It has a hard line connection to the back port on the proportioning valve which will need to come off. The trailer brake add-on 'T' screws into the prop valve, then the original line screws into that 'T'. I've already installed new front pads/calipers, rear shoes/cylinders and bled the entire system with new fluid and have great pedal.

Since the extra connector is right at the proportioning valve, will I need to worry about getting air into the valve and/or master cylinder or will I just need to re-bleed the system and be done?

It looks like the back port may go to the rear wheels only so would I be able to just bleed the rear wheel cylinders or will I end up with air in both front and back?

When I pull the fitting out of the prop valve, is that an open path for the master cylinder to drain or is there a check valve somewhere in the circuit that would keep it from free flowing?

Sorry for so many questions, but being what brings me to a necessary halt I want to get the brakes back to full function. Thanks.