though this bug might've been fixed in 1.13,but if not please fix it mojang,since i believe with a silk touch pickaxe we could still be able to obtain the block.anyways,using this contraption in the right place could result in the block being copied in the place the player wants.furthermore its not TOO expensive,but after all,slime can be found easily in rivers,which arent too rare,neither common.also,idk the crafting of the piston LOL the bug occured in 1.12.2,but the s### JIRA thinks 1.13 was the first ever release of minecraft

video of contraption:https://youtu.be/E3vFA1iEidw

(dont read the video  description,its  the same.)