Yes you can use the same tank for B&W and Colour just wash well after each use. Some of my Patersontanks are over 40 years old and I've never had a contamination issue.

The red colour is a dye in the B&W emulsion nothing to do with what the tanks been used for before. Tmax films have the strongest colour, fix a bit longer than usual which is necessary with Tmax films anyway and extend the wash the colour does wash out. Doesn't need to be running water just leave the film soaking.

Ian