Colonel,
That is very familiar. Following each BCG treatment I had dark red blood and clots 1 to 2 days. Following BCG + Inf treatments there was less blood but more urgency and frequency. These things irritate the bladder as they do their good work.
Just let the care team know what is happening at the start of each appointment ans treatment. Report anything unusual ASAP. I hope it goes well.
Best,
Jack