Summer sq'irkjuice is made from Summer sq'irks, found in the Sorceress's Garden minigame. Level 65 Thieving is required to enter the Summer garden. To make the juice, pick 2 summer sq'irks and use them with a pestle and mortar. You must have 2 Summer Sq'irks and a beer glass in your inventory in order to make the juice.
Picking the Summer Sq'irk will give 60 Farming experience. Drinking the Summer Sq'irk juice will restore 20% of your energy and give you a Thieving bonus of +3. Additionally, 5 cooking experience is gained per Summer Sq'irk juice made.
You can also give the Summer Sq'irk Juice to Osman for 3,000 Thieving experience. Due to the large amounts of experience per inventory, reaching 84k experience per inventory, it can be used to get high levels or even 99 Thieving in a matter of minutes (without counting the time consumed for preparations). Summer sq'irk juice provides the highest Thieving experience of all the sq'irk juices.