Never use Rit in the washing machine. The water doesn't get hot enough, or allow the fabric to soak long enough.
Get another 2 bottles/packets of Rit and a bucket/tub big enough to soak the entire garment.
Pour boiling-hot water into this tub, in quantity of just enough to cover the garment, which should be the water amount for ONE bottle/packet of dye (or less). Add both dyes, stir it well and stuff the garment into it. Leave it until the water's cold, stirring occasionally if you want. Drip dry.
If that doesn't work, there's always the "use india ink instead of fabric dye" method... but that can get pricey.
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Get another 2 bottles/packets of Rit and a bucket/tub big enough to soak the entire garment.
Pour boiling-hot water into this tub, in quantity of just enough to cover the garment, which should be the water amount for ONE bottle/packet of dye (or less). Add both dyes, stir it well and stuff the garment into it. Leave it until the water's cold, stirring occasionally if you want. Drip dry.
If that doesn't work, there's always the "use india ink instead of fabric dye" method... but that can get pricey.