Black Tank Roof Vent and Bathroom Roof Vent Too Close?

Unfortunately, a common layout since both are typically right about the toilet.
And every time you flush, the sudden drop of water into the black tank will push that volume of air out the vent. And if the wind direction is blowing from the tank vent to the open bathroom vent, in it goes. A new vent with a fan might solve the problem, but would require wiring in the electric.