Old School RuneScape Wiki

bucket of sap is obtained by using a knife with an evergreen tree, while having an empty bucket in the inventory.

While many quest guides claim you must get sap from an evergreen, there are also many trees which give sap that are not described as 'Evergreen'. These are typically the slightly taller and pointier trees, and can be told apart by their examine text, which is "A commonly found tree.", instead of "One of the most common trees in RuneScape." It is used in two quests: Icthlarin's Little Helper and The Eyes of Glouphrie. In Icthlarin's Little Helper, you give the bucket of sap to the embalmer. After the quest, the embalmer will buy buckets of sap from you for 30gp each in groups of 1, 2, 5, 10, and 20. In Eyes, you use the bucket of sap with a crushed mud rune to create magic glue.

A very fast way to get the sap is by using the Ardougne Cloak, as there is a tree directly west of the iron rocks that will give sap.