Plain old distilled water from Walmart, under $1 per gallon. On the T105s, when you shine a light in the hole you will see a tube going down from the top of the hole. The tube is slotted. I want the water to touch the bottom of the tube, barely.
Don't remember who recommend this, but buy a weed killer spray bottle from Lowe's or Home depot. They hold over a gallon, are opaque to see the liquid level, and have a screw in pump on top. Remove the spray head at the end of the wand, fill the jug with water, and pump it up a little. When you squeeze the button, a small steady stream will come out the end of the wand. With a small bright light, you can look in the hole and have the wand on the edge of the hole to add water. Looking at about a 45 degree angle is better than straight over the hole. Less pressure is better. If you keep the jug less than half full, you can top more cells between repressurizing the sprayer.
Ted