Purging hydraulic fluid from boom lift

[BeezFun]

I've got a boom lift like this one. I need to change hydraulic fluid, it has several long cylinders and a lot of hoses so I'm thinking it's best to purge the fluid rather than just drain return tank (tank is 2 gal). Can I disconnect suction line from return tank to the pump and put the line in a 5 gal container of new hydraulic fluid and cycle all the cylinders? I'm thinking that will suck fluid out of the container and send the dirty return fluid out the open hole on the return tank into my collection container. The mechanic at dealer said tank contains 90% of fluid in system but that makes no sense to me when I look at the length of hoses and size of cylinders. Thanks for any suggestions.

 

[R W]

May work if you use enough oil.