How do I lower the pick-up tube for my genset

Your Monaco has a separate Pick up tube. At least some Roadmaster chassis do. Regardless, all you do is lift the pick up/sender up and out and add a short length of Hose to the Genset side. But, I would bet the problem is in your tank. I have never seen a Roadmaster chassis with a Genset pick up tube that high in the tank. I would suspect someone has switched the correct pick up tube with the RETURN fuel tube input. THAT would cause your 2/3rds problem. The GOOD news is, you can access the Pickup/sender unit without dropping the tank on Roadmaster Chassis's. You will have the Aqua Hot Pick up tube also if you have an Aqua Hot system. JUST remembered, You have 2 fuel lines going to the Genset. ONE is the supply feed and the other is the return feed. IF those are reversed at the Genset, you will experience your type problem. This can happen when the genset has been pulled to be worked on or the Fuel lines have been disconnected and they are installed backwards. So, I would reverse the Genset lines and then when the Fuel gets below 1/2 tank see if the Genset runs. Doug