thats your flow control valve its there to keep the slave cylinder at the correct pressure so to stop clutch slip. you cant bypass it other wise you might end up having gear engagement issues as you wontbe able to disengage the clutch properly and if you do get it into gear its likely to slip alot. your best to see if theres any part numbers on it then order a new one,
should be alot cheaper than removing the gearbox to do the slave,