I have performed the 50 hour service on my 5145, the biggest headache was the suction strainer...getting the suction tube disconnected ,and yes you must drain all the fluid, there are 8 or 9 drain plugs under the tractor...everything is layed out in your owners manual i have reciepts for everthing and i took photos and videos of everthingi performed step by step ,i drained into a 5 gallon clean pale, then pumped it into two 5 gallon buckets, then when i was done , i filtered the fluid and put it right back in, i spent a couple days on this service in my garage, i just took my time.... if you have any questions, just shoot me a message ,good luck!