I have a couple of buses with the T444E. It's a great engine that has a few myths about it propagating on Youtube. One that is laughable is the HPOP reservoir drain myth.
The way it seems to go is that there is this little known port on top of the HPOP that you can insert a vacuum into and suck out all the old oil that has been sitting in there and boost your performance.
Baloney. You can indeed drain the reservoir, however since the HPOP just takes it's oil from your engine sump supply, it will just fill back up with the same oil it has always been using. The HPOP reservoir is like a teacup sitting in a bowl, sitting in a pot. The oil is pumped from your sump by the low pressure pump and fills the reservoir to overflowing. The overflow just returns to the sump. The HPOP picks up its supply from the reservoir, utilizes it and returns it to the sump.
There is never stale oil sitting in the HPOP reservoir that needs to be cleaned out. The T444 is a well designed engine and the engineers that designed it didn't get their credentials from Warner Brothers. The HPOP reservoir is like a backup sump to prevent the HPOP from running low on oil even if you are cutting a corner on two wheels and all the oil in your sump is up on the side. as if that could happen.
The only time you might want to drain the HPOP reservoir is when you are doing an oil change. That is one place your old oil will sit when you drain the sump. It is not a lot of oil in comparison to the 4.8 Gallons of fresh oil you will add, but if you do drain it, add the amount you remove from the HPOP reservoir to your fresh oil in the sump.
By the way engines with the HPOP system will perform better with clean oil and fresh filters.
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