What type of paint brush should i use to paint the grout between my shower tiles?

i am using a thin brush, but a bit is overflowing onto the tile, is there some sort of sturdy brush or other device i could use to paint such narrow spaces?What type of paint brush should i use to paint the grout between my shower tiles?
To stain (paint) grout you should use an old toothbrush. Cut the sides of the toothbrush off until it is about the same width as the grout joint. Apply stain to the brush then scrub it into the grout.For more infomation see the article below on fixing common grout problems.

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