hpop reservoir draining out

[melmount]

How can the hpop(reservoir) tank drain back to the pan? Bob guzzle mentioned the valve under the hpop or a really worn lpop? I have 117k on it. It runs well, just slightly slow starting. I checked the sight plug. It was close to empty this morning. Looking for how and where I need to look and if theres more then these 2 possibilities? I am sure Bob knows but cant hurt to ask.
this is on an 01 i just bought

 

[melmount]

bump, anyone????

 

[mspainting]

I posted a similar issue & this the responces i got back http://www.superdutydiesel.com/forums/99-7-3l-powerstroke-engine-drivetrain/23276-hpop.html