I am an experienced airsmith so I can tell you that it is not hard and YES IT CAN BE DONE BY YOURSELF but there isnt much point to it.
Let me ask you why you want that? what it will do is keep the liquid CO2 from going into the gun.......HOWEVER, the only way it works iis if you keep your gun level....if you tilt your gun then you will get more CO2 into your gun then if you didnt have the anti siphon tube in it.
My suggestion would be to get an good quality expansion chamber like a 4 or 6 stage.........does a much better job keeping the liquid out of the gun than the tube.
But if you have to have the tube then follow these instruction to a tee.
you will need a strap wrench, regular screw driver, locktight and a vise.
screw the tank onto the gun as it is and make a mark on the tank and the valve for alignment. note the mark must be made as the gun is level (for shooting).
next place the valve into the wrench and secure it firmly in place. secure the strap wrench onto the tank and remove the tank from the valve. on the bottom of the valve should be a set screw that you will need to remove from the valve, this is where you place the tube. make sure when you secure the tube you use locktight on the thresds and you line up the tube nozel with the alignment marks.
then place locktight on the threads of the tank and resure the valve to the tank, making sure that you align your two marks.
then you are done. donot place air in the tank for at least 24 hours as it is airtight and the cold from the CO2 will not cure the locktight correctly.
now your done