J-Lube Powder is a water-based lubricant in powder form.
You mix the powder with water, and the result is a lubricant suited to your needs. A bottle of J-Lube gives between 20-25 litres of ready-mixed lubricant.
Start with 2-3 level teaspoons of powder per 500 ml of water, and experiment to find the mixture ratio that provides the texture you are after.
J-Lube was originally a veterinary product, but is popular with and suitable for fisting, and can also be used for play with all sex toys.