My tie-dyeing squirt bottles often get scummy inside, especially if I've left dye in them for long periods (weeks to months) or used thickener, which gets moldy after a while. Mmmm, yum. I've never been happy with those spindly baby bottle brushes for cleaning them, and a toothbrush often can't get to those scummy spots.
However, I have a bag of old toothbrushes (I just hate throwing things away!), a candle, and some needle-nosed pliers, so it's time to make what I need.
I heat the neck or head of the toothbrush gently over the candle flame. I have to be careful not to get the bristles in the flame, or they will shrivel up and become useless. Occasionally the brush might catch on fire. If it does, I just blow it out quickly and keep working. I'm not worrying about prizes for beauty on this job!
Once the handle plastic has become soft, I grab the head and do the bending with the needle-nosed pliers. I hold the head in the desired position until the plastic has cooled enough to hold its shape.
I modified several brushes to fit different parts of the insides of my squeeze bottles. Here are the resulting brushes. They come in very handy!
If you try this, be sure to work in a safe, well-ventilated area (I did it on the stove with the hood fan turned on full) and remember to wear your eye protection!