Oil line plug caps

You don't  need any caps if you remove the oil lines off the tank. When you normally drain oil the oil in the fittings at the top drian too. If you remove a line just tuck it under a hose or wire to keep it above the tank level. No more oil will come out than a normal oil change. When you unscrew the tank fitting and lift it off you most likely won't see more than a couple drops of oil. Just remember to keep both fittings above the tank top so no oil drains from the hoses. If you allow the hoses to drop down and completely drain then yes you would need to do a purge. The key here is don't let any oil drain from the hoses.

p.s.

If you want you can go to the hardware store and buy a couple of rubber plugs to stick in the fittings when you remove them. I use rubber plugs when I do a 5 year hose change to keep from making an oily mess on the floor.